RE: Renewed interest in SBSP popping up all over the place - SPAC in SPACE

[John K. Strickland, Jr.]

Consideration should be given to the propellant, engine system and power system masses as well as just the Isp. Delta-V values for electric propulsion tend to be much higher than for chemical propulsion, so this is an issue of trade-offs.
If you include use of EM-L1 or high Earth orbit at distances similar to the moon, Oberth maneuver departure to Mars, and single pass aero-capture (SPAC) at Mars, chemical propulsion might be useful for the transit to Phobos, but not to an asteroid.
It is possible, using lunar propellants, to reach Mars orbit from EM-L1 with about 1.3 km/sec delta-V, not including mid-course corrections or plane change if needed. During the trip out, the vehicle would have no return payload so might be much lighter.
On return to the Earth-Moon system, with chemical or electric propulsion, you can also use an Oberth maneuver with a close Mars pass and then SPAC at Earth to get into an orbit ending near the Moon or near EM-L1. The method does require tiny burns to raise the initial orbit out of the atmosphere. Use of lunar propellant for Mars departure makes this method especially favorable. Using SPAC does require the use of small and short high thrust burns.

Also remember that SPAC is a capture maneuver. It is possible to do additional passes to lower the apoapsis from the initial value to whatever is needed, and the higher it is, the less heating on the atmospheric pass. Aero-shields can be used to protect the vehicles during the SPAC maneuvers.

John S


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Subject: RE: Renewed interest in SBSP popping up all over the place

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


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[Tim Cash]

I wonder if we are to the point in design of a wireless power transmission system for space to surface use if we know at least some of the typical power levels and aperture sizes for either microwave or laser transmission systems?  I see one to ten gigawatt for microwave GEO to surface systems quite often.  I see numbers far less than that for laser systems because the larger lasers are in the 50 to 100 kW class arena.  I almost never see hybrid systems with both microwave and laser both being used, probably for good reason.

If we are to replace earth as a point of manufacture and automate the manufacturing process on the moon, deimos, other bodies in space, let us not fool ourselves the power requirements will be quite large, Gigawatts and greater.  I can see why people say this task does not scale very well, one has to start big.  Even so, we are far under the point of moving industry off the Earth any time soon.  This may be a slow process requiring patience for building systems at ever increasing power levels with modest improvements over time.

Tim Cash

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Tim Cash

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[Paul Werbos]

Hi, Tim!

Certainly gigawatts will be needed to impact the main electric power market, or even just the 10% of it I propose as our main target. 

My old papers with Fork aimed at that level, using the type of high power laser most compatible with D-D pellet fusion in space, the main opportunity to do better (eventually) than the usual microwave system design approaches for space solar power. 

It is NOT READY yet to compete with SPS-alpha. I listed it as one of the two "team B" options in my ISDC talk on SSP (attached) last month.

There is a lot of important practical work on lower power lasers for many other applications, but as you suggest, not so relevant to the main SSP electricity goal.

Now that I look back... in my later years at NSF, I contacted Perkins of LLNL/NIF

and others, to explore what new research directions might get us closer to making this "B team" option available. Laser design was a major part of it, but there were also critical issues about how to simulate/model what happens in pellets hit by laser light. That got into a level of nuclear physics I talk about much less lately, because of global security issues. There are many options for high power lasers, and probably ways we could be more strategic about how to develop them. If I were still at NSF, that might still be on my table.

One more "lost world"...

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[Tim Cash]

Paul,

I love the way you cut to the chase on major issues to achieve space based solar power top efficiency, A Team.

I still do not quite understand how the SPS-Alpha is supposed to self-guide the light beams into the "flower" shape unless I am missing some major point on the design.

Is SPS-Alpha a constant aperture design?

I attended the first day of the ISDC 2022 Space Solar Power Workshop ONLY and picked up quite much, spent the last week studying the papers.

As I have said, my best work may not be the design itself, but the support work required to baseline the RFI Environment of any given SPS design.

My best career work lies in this arena between the intersection of theory and test and measurement (lab and field).

I am getting ready to begin to 3D print several flat antennas for 915 and 260 MHz for a balloon flight of software defined radios for my day job at Northrop Grumman, fun!

Take care, and keep up the fight!

Tim Cash

cash...@gmail.com

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Tim Cash

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[Paul Werbos]

https://twitter.com/thinking_panda/status/1534120419929694209

A long-time friend from the great days of Congressman Roscoe Bartlett

alerted me to this important article. I wish I had access to the full paper! 

A KEY IMPLICATION:

The rational best guess, for anyone fully informed on all the details (as I will be happy to elaborate on), is that China is probably very far along, on course, to be able to launch ten times as much mass to LEO or GEO per dollar as we can, which massively changes the balance of power not only for space solar power but for issues like preventing missiles from  causing mass destruction anywhere they are aimed. 

===========

I have already posted enough to back this up on these lists. I owe special thanks to Gary for inviting me to explain in his symposium at ISDC last month. The slides -- which refer to some of the key launch cost issues -- are posted at the SSP link at his build-a-world.org site. Probably he and NSS have the recording of the words which explain all this much more emphatically and clearly.

ON THESE LISTS, many of you know that Musk has promised launch costs low enough to be able to compete in all these markets. The race between SLS and SpaceX is like a race between a snail and a clam; the snail (Musk) is winning, but those rabbits in China have real mammal brains and they are so far ahead in this and some other key sectors... that I am glad I have new invitations to come again to Nanjing and Wuhan, to revisit the 21st century!!!

How to summarize the issues, without overloading peoples' tolerance for technical details?

Above all.. repeated reentry of the whole vehicle, without huge refurbishment costs between launches, depends on whether the primary launch vehicle has manufacturable MATERIALS AND STRUCTURE, able to withstand AT LEAST the thermal, acoustic and mechanical shocks of repeated re-entry. Even now, WPAFB has the only test lab in  the US fully able to test that. I am grateful that Jess Sponable and Mike Snead of WPAFB have been willing to give us their feedback (even if spun a bit on the optimistic or pessimistic side at times), essential to a sense of reality on this. The hot structures illustrated in these slides (for which I have VERY extensive backups and details) were the ONLY ones which had ever passed, when a few years ago I had a chance to visit Dr. Paul at WPAFB and check on what my NSF reviewers and PIs had told me. I have spoken to key Musk people in the Bay area, and they steadfastly did not want this kind of testing or novelty.

The TRUE HISTORY of the HTV-2 debacle is a great piece of evidence as to why we need better testing as a key step in design, and as to how we explain  the failure of NASP to do what was intended (which Boeing could have done on its own with Dana Anderson,

if certain money people had not intervened as they have with SLS). 

The Chinese have been watching all his, and there have been more and more signs that they drew the right lessons and are plowing ahead, as they did with advanced AI.

My slides from China in 2017 https://photos.app.goo.gl/Ph3NSbTHfJMJ57Fj7

do not show the many more advanced things I have seen with my own eyes there -- but their accomplishments in AI and quantum technology show it would be surprising if they DIDN'T have competence in catching up to the very best in launch technology as well.

Our sources in India have certainly sent us information to that effect, especially from Sichuan province, the center for aero technology which they do not want to show the Russians (on display in Harbin Beijing and Manchuria, all of which I have visited). 

I AM NOT PROPOSING HOSTILITY TOWARDS CHINA, JUST RATIONAL BALANCE, AS VON NEUMANN would advocate. We are too far behind to get ahead, but it is essential to peace and to balance and to the world economy and ecology that we fully mobilize the launch technology would let us get back into the game. 

Best of luck to us all. We need it.

     Paul

[John K. Strickland, Jr.]

Note that I was not advocating immediate use of asteroid resources, but rather bringing up major points which would affect the economics of such an effort.

Note that we have already visited and brought back samples from asteroids so there is no doubt that asteroid mining is physically possible.  What is in doubt still is the economics, since the equipment to enable such operations (both mining and transport of product) is either still in development or development has not even started (unless it is in secret! ) The first SPS units should be built of Earth materials simply due to the urgency of developing a viable, provable SPS design.  Once we have one or more such designs in actual operation, it would be possible to transition to asteroid-like sources if the economics are favorable.

 

John S

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[je...@sponable.space]

Paul

I agree that China is well ahead, but there are some subtleties to the story.  I would agree that although SpaceX is well ahead on the reusable launch vehicle front, China is investing huge funds to catch up and surpass them.  For example, I count at least six reusable launch programs in China (most VTOL), either funded by the government or the commercial sector (hard to tell the difference in China).  Two of note are a vertical take off and horizontal landing demo they FLEW a while back.  A bit akin to my old DARPA XS-1 program, only where DARPA/AF refused to adequately fund the program, China just plows ahead.  There is also a commercial venture to do a point to point boost glide transportation system (this may sound crazy it is not – done right such vehicles can outcompete subsonic jets both on environmental cleanliness and potentially cost.  Bottom line – a lot of Chinese investment is going on to try to catch SpaceX.  The danger is if Elon has miscalculated and Starship is too big deliver a reasonably near term demo and follow on capability then China will roll on by US.  We do have some other commercial companies doing reusable launch: Blue, Stokes, Relativity, RocketLab, Venus, etc.  However, they are all far behind.  And if the market goes south, maybe further yet.

 

Where China is way ahead is boost glide weapons.  Their DF-17, 21, 26 are theater range maneuverable weapons with a reach as far as Guam.  They also have an operational air launched ISR platform, WZ-8 that flies a boost glide trajectory for ISR then recovers with a horizontal landing.  So if their eyes in space get poked out China will keep on trucking.  They are clearly preparing to dominate the entire South China Sea area.  Late last year they flew what was described inaccurately in the press as a Fractional Orbital Bombardment (FOB) system. In actuality it was a global reach boost glide weapon.  I believe the reason they flew around the earth once before reentering and gliding was so they could do their glide and terminal maneuvers on their Chinese test range (hard to test boost glide systems within continental ranges as we learned on HTV-2).  What is especially concerning is that they were reasonably successful on their first flight, while HTV-2 failed twice (despite DARPA claims that they were partially successful – basically we proved the launch and separation systems).  Once again, DARPA got tired and stopped funding.

 

Instead we are desperately trying to catch up with CPS and TBG both theater range systems akin to China’s DF-17, 21,26.  It sounds bad but it is not hopeless. We flew many similar systems in past SUCCESSFULLY – BGRV, AMARV, SWERVE, etc.  And the first two were essentially global reach systems. I worry the only answer is to set up another SDIO like organization and dig up people who can do this who are not mired in the bureaucratic incompetence of the Pentagon.  Truth is bureaucracies ossify over time – and we are very ossified, maybe calcified at this point!  Conversely, China is where we were in the 1960s – try it and if it doesn’t work try it again!

 

The real future of warfare (and likely commercial transportation) will be defined by who figures out how to put these technologies together.  Hypersonic reusable launch using simple rockets (don’t get sucked down the scramjet rabbit hole unless your prepared to invest orders of magnitude more, and still willing to accept failure), and boost glide weapons will open up a new era of global reach capabilities.  On the commercial front, every indication in my recent analysis suggests it may turn out that flying faster, further, cleaner and greener using rocket vehicles may outcompete today’s jets (and yes I know this sounds counterintuitive).  Right now, I’m not placing a bet on who will take the future.

 

Bottom line:  if Starship works we will be in good shape on the reusable launch front.  Regarding hypersonic weapons we are way behind and pursuing foolish implementation CONOPS that will be unbelievably expensive (air launch, sea launch, ground launch – all with giant costly expendable boosters relative to the simple glide vehicle). 

 

But this is just my opinion!

 

Cheers

 

jess

 

 

 

 

 

 

 

From: power-satell...@googlegroups.com <power-satell...@googlegroups.com> On Behalf Of Paul Werbos
Sent: Wednesday, June 8, 2022 3:17 PM
To: John K. Strickland, Jr. <jkst...@sbcglobal.net>

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[Tim Cash]

Jess, Paul, John, Gary et al,

I am doing my best to pick up the slack of catching up with China, but I am one person, an old guy, what can I do?

I have learned quite a lot from this group, but I know what I know and I sure know what I do not know just as well.

I can try to push ahead with bravado, but my contacts in this group may be my saving grace.

Yes, it does very well appear I will get a pivotal role in beamed power, I have opened my mouth to the right people, both in these circles at  home and abroad, as well as within Northrop Grumman.  I also am getting side work in a major power distribution system project, and I understand this is a major piece of space solar power.  Northrop Grumman is an expert in this arena, not me, my company.

This is all I can say about the topic at present.

Other groups are good at what they do.  It is a matter of pulling in all the experts, and the pieces of technology, and then doing our systems engineering magic.  Just keep saying to ourselves, we are the ones that landed on the moon, yes we can, yes we can.

However, making one working prototype is a far cry from cranking out numerous powersats, that is for sure.

I thank all of you for your guidance.

Timothy Cash

Senior Systems Engineer

cash...@gmail.com

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Tim Cash

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[je...@sponable.space]

Tim

All good.  I offer my opinion because if you don’t understand the problem, then finding a solution is problematic.  Keep pressing on your fronts, as we all will.  The future is a bit scary, but still unrolling – nothing set in stone yet!

 

jess

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