Re: Renewed interest in SBSP popping up all over the place

[Keith Henson]

> This looks like building a head of steam.
>
> If we want to build hundreds of GW of SBSP, then we simply *have to* look to extraterrestrial supply of construction and component mass. Otherwise, the lift reqd is massive, even tho Elon will have reduced the cost-per-kg to the $100-or-so range. The enviro impact becomes very non-negligible (ref Henson worrying abt killing the ozone layer etc). Political pushback??

NOAA figured out that even a million hydrogen-burning Skylon flights
per year (1.5 million tons) would not do too much damage to the ozone.
There is a pointer to the report they wrote off the design to cost
page. NOAA would be happy to redo the study for the methane burning
StarShip, but they would need SpaceX to ask and cooperate.

> Remember, very early studies showed a tenfold earth-launch reqt reduction if structural mass sourced from (eg) the Moon. This is a game-changer observation.

I think you are talking about O'Neill's 1975 paper in Science. I
posted a copy of it in the Power Satellite Economics group recently.

> I assert that there is a significant probability that Deimos might be a source of iron, carbon (hence steel), and water (hence propellants), and from C and H2O, high strength longchain polymers. From the silicate component, silica for solar cells.
>
> I ask: *might Deimos be the place to construct multi-GW SSPSs, and then fly them back to GEO (or other chosen Earth-orbits)??* Note that SSPSs can also address the Mars city power reqt., as Mars synchronous orbit is a mere 90 m/s dv down from Deimos.
>
> The workers would have a solid ‘shipyards’ surface to work off,

I am not sure this would help, though I don't know for sure. The
escape velocity off Demos is low, but assuming you had a power
satellite on its surface, how do you get it off? Perhaps a tether
with a big rock on the end.

> and habitat buried for radiation protection. At a large scale, and longer term, you would have buried, *rotating*, habitat for earth-normal g.
>
> No radiation worries, no Kessler/ collision worries. Human hands-on.

How do you avoid radiation and still have hands-on?

> Supports Mars colonization. Supplies longterm Earth Power. Moves large construction activities into space.
>
> Optimism for the future, supports STEM future hitech jobs and ancillary activities etc.. Mitigates multiple one-planet existential risks. What not to like?
>
> Any showstoppers??
>
> Talk to me.. I may well already have responses…

I certainly agree with you that Demos is better than the moon. There
may be better places though.

Keith

> Mark
>

[Peter Garretson]

Not the guest time someone has thought along these lines:

I wish NASA was sponsoring work along these lines!

https://noconsensus.wordpress.com/2009/09/02/the-solution-to-future-energy-needs-and-global-pollution/

The Solution to Future Energy Needs and Global Pollution

Leonard Weinstein, Sc.D

April 19, 2009

Introduction:

There are two problems quickly becoming apparent that will have a profound effect on modern civilization. These problems are:

1) Increasing energy costs due to limited availability of fuels

2) Increasing pollution due to increased development and energy use in the world

The problems are highly interdependent. They clearly derive from the burning of fossil fuels, which are finite and in some cases are unable to be obtained in quantities fully able to meet demand.

How we satisfy our present energy needs: 

There are two distinct categories of energy needed for modern civilization. The first of these is the energy needed for fixed locations (e.g., homes, businesses). This includes electricity, oil, gas, and solid fuels (e.g., wood, coal) for heating, cooling, lights, motors, etc. The second of these is required for transportation (i.e., cars, trucks, trains, planes, and ships). This is currently mainly liquid fuels (gasoline, fuel oil, alcohol, etc.), but can include compressed or liquefied gases (methane, propane and even Hydrogen). There are some vehicles that use grid electricity for power (trams, and some trains), but these requires a limited fixed travel route over the ground.

The vast majority of the energy needed for fixed locations is derived from fossil fuels, with lesser amounts from hydroelectric and nuclear electric generation. Other sources of power also are available, such as Geo-thermal, wind power and Solar. The main present source of electrical energy production in the world is from coal-fired steam turbo-generators. The large quantities of coal available (including huge reserves) and low mining cost, make it an especially low cost source of power. Coal was even used for many years as the main source for heating. However, the need for individual bulk delivery to homes, the difficult method of fueling the fire (cleaning out ash and shoveling coal), and the dirty smoke led to use of more convenient and cleaner fuels and sources of power. Present homes and businesses now mainly use oil, gas, or electricity for heating, and electricity from power plants for other energy needs (cooling, lights, powering motors, etc.). Natural gas is gaining in popularity due to its increasing availability and relatively clean burning, and also due to the fact that it can be continuously delivered via pipelines.

The energy for transportation is mainly derived from fossil fuels, with the vast majority using oil derivatives (gasoline, kerosene, jet fuel, etc.). Use of bio-fuels such as ethanol, plant oils, and plant-based methanol are increasing in importance, but are still a small fraction of the total fuel used. A major driving factor for fuels for transportation has been cost, and cheap oil has satisfied this need well until recently. The increasing oil consumption of countries that were previously third world (mainly China and India), and limited easily obtained increased oil production (and finite reserves) has put the pressure on obtaining alternate sources of fuel. The huge oil sands deposits located in North America are becoming a major source of oil. Other potential sources including shale oil and synthetic oil made from coal are not yet competitive, but probably will be so in the near future.

The problems with present sources of energy: 

Burning fossil fuels produces Carbon Monoxide, Nitrous Oxides, Sulfur Oxides, and particulates (including heavy metal contamination), which all negatively affect the atmosphere to some extent. Carbon Dioxide is also produced in large quantity, but this is not a negative factor as the others are. Burning coal also produces large amounts of waste ash which is difficult to dispose of safely. In addition, the present easily obtainable oil reserves are limited and might not last too much longer. Since oil is the main source of fuel for transportation, this is particularly significant. Alternatives such as synthetic oil based fuels made from coal or other sources are both more expensive, and also will eventually be limited.

The use of renewable fuels such as ethanol, methanol, and biologically produced oils appears to be an attractive solution, but many issues have arisen including the limited amount of land that can be dedicated to production without negatively impacting food production and costs. In addition, recent analysis indicates that converted land (converted from forest or multi-crop activity) may actually produce more pollutants due to the conversion than is reduced in the vehicle by use of the alternate fuel.

Nuclear fission power has its own problems. Licensing and building reactors take a very long time. If the fuel were used directly (non-breeder reactors), the finite Uranium sources would limit the available operation in a relative short time (several decades). Going to breeder reactors can greatly extend this time, but these reactors produce Plutonium, which is very toxic and dangerous. Getting rid of reactor waste products is a major problem. One final problem is due to the need for large quantities of cooling water, which can exacerbate the existing problem of stretched water supplies. If fusion energy were available, it would have some of the same problems as fission power plants, but it is not even available.

While hydroelectric, Geo-thermal, wind and Solar generated power do not have the polluting problems of the previous techniques (but may have other problems) and do not get used up, they are also limited in location, magnitude, and in the case of wind and Solar, are limited in production times. Hydroelectric and Geo-thermal power are very limited in generation capacity. Unless far more practical energy storage and long-range distribution systems are developed, wind and Solar will also remain limited to a small part of energy production.

Some features of ideal solutions to the energy problem: 

A source of energy for power for stationary location and a source of fuel for transportation are needed that satisfy the following requirements:

1) A source of energy that is non-polluting of CO, NOx, Sulfur oxides, particles, and that does not have large thermal waste

2) A continuously available source of energy in all weather

3) A source of energy that can be available without long-range transmission needs

4) A source of fuel for transportation that is continuously available

5) A type of fuel that is minimally polluting

6) A type of fuel that can be transported easily

Solutions to the energy and fuel needs: 

One solution (and in fact is the only one that has been proposed to meet the energy needs that satisfies all of the requirements stated above) is to make an array of Solar power satellites in Geosynchronous orbit to beam microwave power to receiver areas at numerous locations on the Earth. This solution has been studied in considerable detail, and would be practical if it could be done at low enough cost. Unfortunately, lifting all of the material directly from the Earth would be far too expensive at present costs, and would still be too expensive to be practical even at the projected lower cost of the next several generations of lifters. A possible way to bring the cost into a reasonable level might be use of in-situ obtained material from space. One possible scenario of how that could be done is shown in a later section.

Most transportation means, with the possible exception of aircraft, that also satisfy all of the above limitations, are probably limited to electric motor driven propulsion. Aircraft might still have to use hydrocarbon-based fuels, and are not included in the present proposed solutions. The transportable electric power would either have to use storage batteries, or fuel cell electricity generation. Energy for recharging the batteries would come from the Solar power satellite system. A compact and non-polluting storable form of Hydrogen would be needed for the fuel cells. Reformulating hydrocarbons are thus not considered, since they still use fossil fuels. Possibly the best form of hydrogen storage might be in the form of liquid Ammonia, which has about 1.75 times the volumetric Hydrogen content as liquid Hydrogen, and which can be kept liquid at room temperature and modest pressure. The Ammonia would not be made from natural gas or using electricity from hydrocarbon burning power plants as is presently done, or the pollution would still be a problem. The energy from the Solar power satellites would be used to electrolyze water and purify Nitrogen, and the Hydrogen from the water would be combined with the Nitrogen using the Haber process. The liquid Ammonia could then be shipped by truck or rail, or by pipeline, to the locations where it would be dispensed. Use of a Nickel catalyst has demonstrated over 99.5% conversion of the Ammonia to Hydrogen and Nitrogen in compact reactors. Most of the residue can be easily chemically removed from the exhaust stream to make this a practical source of Hydrogen for the fuel cell.

Cost Effective Solar Power Satellites: 

Obtaining power from large solar cell power collectors in GEO and beaming the energy to selected locations on Earth using microwave energy has been extensively studied. This produces no pollutants, and would generate very little thermal waste energy. The technical problems have been extensively examined and do not seem to indicate stoppers. However the present high cost to lift all materials from Earth to GEO prevents this approach from being practical with that approach. If it became possible to make these solar power satellites cost competitive, a significant portion of the electrical power needed on the Earth could be obtained from space. In addition, the power could be directed to many regions otherwise difficult to reach. The present sections suggests a possible way to develop the power satellite capability at a competitive cost if certain assumptions can be demonstrated to be valid.

The first issue to be examined for potential space solar power is the type of power collector and generation system to be used. While solar concentrator based systems could be made very lightweight, and the high intensity used to either illuminate concentrator solar cells, or even make steam for turbo generation, the need for massive waste-heat radiators would lose the mass advantage originally obtained with the concentrators. A very low mass to power radiator concept, practical at very large-scale, is described in an unpublished paper by the present author (but available on request) “Low-Mass Free-Piston Space Radiator”. However, even for that very low mass radiator version, the radiator mass to waste power eliminated would be > 10 kg/kW at the temperature required for solar cells. Since the waste heat is about 2/3 of the total input energy for a reasonably efficient system, this would require a radiator system mass to useful output power ratio of over 20 kg/kW. When the solar concentrators and cells along with the support structure and power converters are included, the ratio is even worse.

There are present prototype versions of solar cells that mass less than 1 kg/kW, and produce about 140 watts effective net output per square meter in space. While the cells are only about 10% efficient, it is the mass to power that is critical, not area of cells needed (space is BIG). These cells would not need separate radiators to remove excess heat while producing electricity! The converters and microwave transmitters needed to send the power to Earth would generate some waste energy and would need radiators, but at a fraction of the total power produced, and at fairly high temperatures, so much smaller versions of the low mass radiators could be used for a far lower total mass. The additional support structures, transmission means, and radiators would probably about triple the mass/kW over the cells alone, so I use a value of 3 kg/kW produced power as possible (about 1/7th the ratio of the concentrator versions).

The greatest driver of the present high cost of space power satellites is the high cost of lifting payload from the Earth’s surface to GEO. Present costs run >$12,000/kg to lift payloads to LEO (and more than double that for Shuttle), and about 3 times this cost to lift payloads from LEO to GEO. This cost of over $48,000/kg to GEO is the limiter for this approach. The next generation of heavy lifter could cut this cost considerable. It would not be unrealistic to assume $3,000/kg to LEO and thus $12,000/kg to GEO as possible in the reasonable future. These optimistic future rates will be used next to estimate how expensive solar cell based power satellites might be able to be made, using Earth to GEO lift.

In order to estimate the cost, it is necessary to make realistic estimates of the mass of power collectors and converters. The cost of assembly, maintenance, and the cost of ground facilities also need to be estimated. The lift cost to GEO using the projected lower cost Earth to space. Heavy lifters (at 3 kg/kW) would thus be about $36/Watt (it would be over $144/Watt with present best technology). The solar cell manufacture cost on Earth might be about $1/Watt in very large quantity, and the ground stations to receive the energy could possibly be made for $1/Watt. The initial design and hardware cost is also assumed to add about $1/Watt for very large systems. The assembly, repair, and operation cost are most difficult to guess, but I am assuming $4/Watt for 20 years of operation. The total of the above is $43/Watt, of which $27/Watt was needed to lift LEO to GEO.

It should be observed that one Watt of continuous delivered power for 20 years yields 175 kW-hrs of total energy. It thus appears that the power cost could be about $.246/kW-hr. This doesn’t include financing cost, and profit. For the present examples, I assume these double the power cost to $.49/kW-hr.

The real advantage of space based solar power would not become convincing unless much lower delivered cost could be achieved. The only realistic probability to accomplish that would be to obtain in-situ materials to make the solar cells and support structures in space, as well as obtain the propellant to put them in GEO. The critical point is to obtain this material and capability at low enough price. The most plausible places to obtain the materials are the poles of Luna and the moons of Mars. There are reasons that I think the best source of materials is the moons of Mars, and for now I am just assuming the larger moon of Mars, Phobos, is selected as the source of the materials.

There are several critical materials needed to make power satellites in GEO from mostly in-situ obtained sources. The one needed in largest quantity would be propellant for orbit transfers. Water is almost certainly the raw material that would be used to make the propellant, and could probably be obtained from under the dust layers of Phobos (see appendix). Energy to obtain the water, and to electrolyze the water and liquefy the oxygen and hydrogen would be needed in large quantity, and would most likely be obtained with fairly large Solar cell arrays (but much smaller than for the power satellites). These could be manufactured on Phobos using power from a smaller array carried up from Earth (bootstrapped).

The second greatest quantity of material needed would be that required for the substrate of the Solar cells. One substrate possibility is a very thin metal foil. The metal (Iron and Nickel) could also probably be obtained from Phobos. Support structures, energy converters, microwave transmitters, and other materials needed for the power satellites may be made from a mix of parts, some of which may be brought up from Earth, and some made in-situ, depending on complexity to make and lift mass trade-off. The quantity of silicon and the trace impurities needed for the outer coat of the large arrays of amorphous multilayer solar cells in the power satellites is far smaller than the quantity of water, substrate material, and structural materials, and could be obtained directly from Earth.

For the following example, a sufficiently large number of Solar power satellites is assumed to be made so that the initial cost of establishing a mining facility on Phobos, and the equipment development costs and factories in space costs are spread over a large number of power satellite systems. The substrates and solar cells would be fabricated at GEO. As in the direct lift example, the mass needed in GEO (not including factories or worker habitats) to produce delivered energy is assumed to be 3 kg/kW.

Costs from previous major space programs, but adjusted to the projected lower lift cost levels expected, were used to make a conservative estimate of costs for a large capacity facility that could be developed, built, and supported over 20 years at Phobos, with the required in-situ mining and shipping capacity. The factories needed to manufacture the cells in GEO would also have to be developed and lifted from Earth to GEO. The cost over a period of 20 years to develop and make the facility, and manufacture and maintain the power satellites is estimated to be $6/Watt. When ground base cost of $1/Watt, and development costs of $1/Watt are added, the total cost comes to $8/Watt. This would result in a cost of power of $.045/kW-hr, and retail $.09/kW-hr.  It would be far more reasonable compared to a fully developed system lifted from Earth if this were possible. However, this approach is still associated with large initial technical uncertainty and very high up-front costs.

One or more missions to Phobos would first be needed to assure the practical availability of the water ice and also the availability of Iron and Nickel (as metal or magnetic oxide). A much smaller prototype power system would likely be made first to solve the technical problems and assure there are no unexpected surprises. If continual increased production of power capacity went on, the unit cost would come down even more, since most of the added mass would not be lifted from Earth, and the established bases and factories could be relatively cheaply expanded. These are actually the main reasons that in-situ sources of material are far better in the long run than lifting most of the material from Earth. If a significant fraction of the factories and support structure were made in space using the in-situ obtained material (rather than making them on Earth then lifted), the cost could be even lower, since the limiting main cost is lift from the Earth surface. A delivered power cost comparable to or possibly even lower than present low cost generation should be possible at large enough scale. It seems to me that this approach holds promise to eventually solve Earths energy problems at low cost, and with no pollution.

The conclusion I draw from the estimates is that even  assuming lift costs to LEO are reduced to $3,000/kg in the near future, direct lift of material for power satellites would still be too expensive to be practical. Considering the high risk and large required up-front cost, this approach may not be too attractive. However if most of the material is obtained from the moons of Mars, the cost could conceivably come down to a much more acceptable level. The use of in-situ materials also would significantly lower the cost even more as the scale of production increased. The availability of water and raw materials on these moons has to be examined before any significant movement can be made in this direction, Manufacturing solar cells might actually be much easier in space due to the availability of vacuum for vapor deposition on low mass substrates. The largest masses needed for the cells are the substrates and support structures. The remaining large problems are mainly the need to develop in-space mining, large-scale transportation, and manufacturing facilities. The limited transfer times and long transfer distances from Mars to Earth are factors here, but I have developed a concept that may make it far less of a limitation (contact author for details). The appendix makes a case for the use of the moons of Mars as the source of materials and selects Phobos as the preferred source.

Appendix:

Abstract:

The two moons of Mars appear to be captured asteroids with composition similar to class C asteroids found mostly in the outer part of the belt between Mars and Jupiter. The measured average density is less than 2 g/cc for both moons. This seems to imply that there is either a loosely packed rubble pile core, or high void fraction (porosity), or that a high fraction of hydrates and water ice is present in a solid core. A very strong argument can be made that the rubble pile or high porosity core is not a probable configuration, although a loose rubble collection on the surface can occur. It is most likely that the interior of these moons is a solid core with about 50% water ice and hydrates (from the need to match the observed densities). The near surface ice would evaporate this near the Sun, and leave a thick layer of fine dry dust on the surface. Calculations indicate that the rate of vapor diffusion through an overlay of loose dust may limit the ice loss rate sufficiently to allow the core to retain a large fraction of water ice, even over billions of years.

Density of Phobos, Deimos and some asteroids:

Recent space probes orbiting Phobos and Deimos, which are thought (with a high probability) to be carbonaceous chondrite asteroids (class C), were able to determine their mass. Since their size is also known, their density was fairly accurately determined. Phobos which is 26 X 18 km has a density of 1.9 g/cc, and Deimos which is 16 X 10 km is 1.75 g/cc. Combining the measured size of some other asteroids-with recent measurements made either by examining the orbits of small satellites around the asteroid, or made by observing orbit perturbations, have fairly accurately determined the average density of these objects also. Generally, measurements made on carbonaceous chondrite asteroids have resulted in lower densities than expected. For example 253 Mathilde, which is 66 X 48 X 46 km has a density of 1.3 g/cc. 45 Eugenia, which is a class FC, 226 km in diameter, has a density of 1.2 g/cc. Even giant 1 Ceres, also a class C that is 960 X 932 km, and is the largest known asteroid, has a density of only 2.05 g/cc. The most accurate measurement for a Stony (class S) asteroid is for 433 Eros, which is 33 X 15 X 13 km, and which has a density of 2.65 g/cc. The expected density for stony asteroids seems to be close to the expected value for nearly solid stony objects (i.e., 2.5-3 g/cc).

Carbonaceous chondrite asteroids with low density may have a large fraction of water ice:

If the asteroids were formed far enough away from the Sun, it is likely that they would have formed with a large fraction of water ice, with small particles mixed in. If the ice rich objects then were perturbed to be closer to the Sun, but did not come in too close, evaporation would remove volatiles close to the surface, leaving a crust of nonvolatile materials such as dust (including carbon compounds), and possibly some captured rock and metal chunks. The fine powder in the surface crust would act as a vapor diffusion barrier. Calculations made for such objects at the distance of Mars, using a surface texture comparable to sand, indicates that even at a thickness of one km, the surface would prevent the ice from evaporating for several billion years. Finer grained dust would not even have to be that thick to hold the vapor. Assuming that the asteroids solid cores are mostly a solid frozen mixture of dust particles, ice, and hydrates, they would have to be near 50% H2O content to have the a density just below 2 g/cc, and much higher H2O fraction for even lower densities. The presence of water ice and hydrates, along with Iron, Nickel, Carbon, and Silicon would satisfy the material needs for the Solar Power Satellites, and propellant to transport it to GEO.

[k.a.c...@sympatico.ca]

> > I assert that there is a significant probability that Deimos might be a source of
> iron, carbon (hence steel), and water (hence propellants), and from C and H2O,
> high strength longchain polymers. From the silicate component, silica for solar
> cells.
> >
> > I ask: *might Deimos be the place to construct multi-GW SSPSs, and then fly

> them back to GEO (or other chosen Earth-orbits)??*...

As it happens, I recently led a study of an Earth-GEO-to-Deimos mission, using electric propulsion. This included a very detailed study of trajectory optimization to minimize propulsion subsystem mass, including propellant mass plus propulsion system dry mass plus associated solar array mass to run the electric engine; this optimized for using a xenon Hall thruster with an Isp in the range 1500-1800 s. The delta-V for that outbound trajectory about 9.5 km/s; I expect it'd be similar coming back from Deimos to GEO (we didn't actually study that case, so that's TBC). For a system dry mass of about 115 kg, propellant mass ranged from 102 to 111 kg (depending on which launch window we chose, we looked at several from 2026 to 2033); wet:dry mass ratio ranged from about 1.88 to about 1.96.

So, for an SPS launched from Deimos, you'd need about the same amount of xenon propellant as the SPS's dry mass, to get to GEO. Deimos of course does not (as far as we know) have any xenon; oops. Maybe it has water; if you run water through microwave electrothermal thrusters (something I've studied in quite a bit of depth over the years), you maybe could get half that Isp. That'd increase the amount of propellant needed by a factor of 1.88^2 to 1.96^2, for a wet:dry mass ratio more like 3.5-3.8 --- i.e., for each kg of SPS dry mass, you'd need about 2.5-2.8 kg of water propellant. Not crazy impossible, but still quite Deimos would need to have a *lot* of water to be a useful SPS factory. (Unless you can think of a better locally-sourced propellant.)

- Kieran

[k.a.c...@sympatico.ca]

Mark;

(When I hit "reply all", I didn't notice that "all" was a very large number of people. I hope that "all" don't mind a bit more in the way of orbital mechanics details...)

You wrote:

> I now remember that you told me some months ago that you were planning to
> do this exercise with your students, and I think I held back because my own
> thoughts were too embryonic at the time. I certainly wasn’t thinking at that
> stage in any detail about SSPS return to Earth-orbit from Deimos, but rather, of
> return of bulk propellant either using chem propulsive Oberth burn to do
> capture, or Lunar Flyby capture..
>
> So: what about lunar flyby capture? Coming back non-impulsive suggests to me
> that there is scope to design the Earth-approach to enable such capture, as v-inf
> in the non-impulsive case can be much less than Hohmann v-inf, and the result
> could be insertion into a very high HEEO from which to work down to GEO
> incrementally.. and a significantly reduced total dv for return. Maybe halved, cf
> your TBC number based on outbound..

A bit more detail on the delta-V budget, from GEO to Deimos, for the 2028 Mars launch window:

- Earth-escape - Spiral: 2.6 km/s
- Trans-Mars Injection: 2.86
- Mars orbit matching: 2.97
- Mars descent - spiral: 1.08
- Total = 9.51 km/s

The spirals in and out can be reduced in delta-V somewhat, by using thrusting near periapsis; the shorter the orbit-arc near periapsis you do thrusting, the closer this approximates the impulsive-escape delta-V, at the cost of taking a longer time. E.g., in one solution studied, the Earth-escape delta-V can be reduced to 1.81 km/s, but escaping then takes 426 days, versus 117 days for the spiral-escape. (The durations depend on the electric engine's thrust, and the spacecraft's total mass, of course, so would vary from one s/c design to another; these numbers are exemplary.) Another case using twice the thrust took 192 days to escape, with 1.78 km/s delta-V.

We didn't analyze the case where a lunar flyby was used to reduce delta-V. But from the budget, you can see that only has scope to reduce the Earth-escape part of the delta-V; even if you could cut that in half (which I doubt a lunar flyby would actually achieve, when doing a low-thrust trajectory), you'd still have about 8.2 km/s total delta-V, which is 86% of the above total. So, not much scope to reduce the total delta-V that way.

The real delta-V savings comes from doing your burns as deep in the gravity well as possible, to use Oberth's effect (you may recall that Grant and I debated this at length for asteroid missions, Grant opting for this strategy). But that requires high-thrust (basically impulsive) propulsion, which means chemical (or maybe someday nuclear) propulsion, not electric. Which means chemical propellants. If there's water at Deimos, you could electrolyze that to H2 and O2, which'll give you the highest possible practical chemical Isp --- although it'll be even lower than the MET thruster/water Isp I alluded to, by a factor of about 2, and hence what you save in delta-V in Oberth effect will be somewhat (maybe completely) offset in mass-fraction by the rocket equation --- would have to run some numbers to check that. Also, storing the cryogenics for the ~ 9 months of the mission is beyond current upper-stage thermal control technology (although solvable in principle with careful thermal engineering that might not mass too much, plus electric cryo refrigeration that would have some mass impact, largely due to the large radiator needed).

- Kieran

[Keith Henson]

Re electric thrust engines, if you are moving a power satellite
around, the attached might be considered.

The guy who runs it said 70% of the 50 MW going into the thing comes
out in the beam as Ke. The rest comes out as heated water.

Ke = 1/2 mV^2 For a 1 kg/sec feed, the exhaust velocity should be
around 8367 m/s

Keith

[k.a.c...@sympatico.ca]

Keith;

 

You wrote:

 

 

> Re electric thrust engines, if you are moving a power satellite around, the

> attached might be considered.

>

> The guy who runs it said 70% of the 50 MW going into the thing comes out in the

> beam as Ke.  The rest comes out as heated water.

>

> Ke = 1/2 mV^2  For a 1 kg/sec feed, the exhaust velocity should be around 8367

> m/s

 

Do you have any further info on this engine? (The pretty picture is nice, it'd be good to get some woeds/equations to go with it 😊).

 

- Kieran

[Keith Henson]

> Do you have any further info on this engine? (The pretty picture is nice, it'd be good to get some woeds/equations to go with it 😊).

It's not actually an engine, it is the gas heater for a reentry testing facility

https://en.wikipedia.org/wiki/High-Enthalpy_Arc_Heated_Facility

It's been a few years since I ran the spreadsheets, but as I recall,
they optimized for moving power satellites at around 20 km/sec exhaust
velocity. They make sense when you have the output of a power
satellite available.

Keith