Dumb SS1 questions
Scott Moore
1. assuming the next "big prize" would be an orbital vehicle, what is the lowest
altitude an object can be orbited at, if only for a circuit or so ?
2. If SS1 wanted to go somewhere instead of straight up, would it be able to,
say, cross the United States at several mach, above the atmosphere ?
3. How much bigger (more thrust) would SS1 have to have to achieve orbit ?
Thanks.
Henry Spencer
Scott Moore <sam...@moorecad.com> wrote:
>1. assuming the next "big prize" would be an orbital vehicle, what is the
>lowest altitude an object can be orbited at, if only for a circuit or so ?
At about 150km it's marginally possible. 200km is more comfortable.
Reaching orbit is mostly a problem of horizontal velocity, not altitude.
The big problem is not getting up to orbital altitude, but accelerating to
about 8km/s once you're there.
>2. If SS1 wanted to go somewhere instead of straight up, would it be able to,
>say, cross the United States at several mach, above the atmosphere ?
No. The artillery rule of thumb is that maximum horizontal range is twice
the altitude reached when fired straight up, which would give SS1 maximum
range of only a couple of hundred kilometers. The wings would improve the
situation somewhat, but still, this is not a transcontinental vehicle.
>3. How much bigger (more thrust) would SS1 have to have to achieve orbit ?
It would have to be completely redesigned. Modest upgrades to its engine
hardware could probably get it to orbital altitude, but there's no way it
can possibly carry enough fuel to accelerate to orbital velocity.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert | he...@spsystems.net
Mike Miller
> If you can forgive a dumb space question or two:
>
> 1. assuming the next "big prize" would be an orbital vehicle, what is the lowest
> altitude an object can be orbited at, if only for a circuit or so ?
At 90-100 miles, drag should be low enough to complete one orbit.
> 2. If SS1 wanted to go somewhere instead of straight up, would it be able to,
> say, cross the United States at several mach, above the atmosphere ?
If you go straight up...well, you go straight up, with no sideways
velocity to cover any distance over the ground. You need some
horizontal speed, too.
> 3. How much bigger (more thrust) would SS1 have to have to achieve orbit ?
SS1 had plenty of thrust - after all, it went up at first, not down.
The issue is more a matter of "how much fuel is needed to get to
orbit?"
Orbital velocity is a matter of moving far enough sideways to avoid
the horizon when gravity pulls you down. What SS1 did is not approach
orbit. Rather, it approached space - it got above the atmosphere.
That's a nice step toward orbit (because atmospheric drag will slow
you down and thus hit the horizon), but it's just a small step.
The big step is moving fast enough to miss the horizon.
That involves moving tangent to the ground at about 17500mph for a low
orbit. Another 2000-3000mph is wasted going up and getting above the
atmosphere.
To get to orbit, a rocket with highly efficient engines (unlike SS1)
would need about 90% of its mass to be fuel and oxidizer. SS1 would
need about 95-97% of its mass to be fuel and oxidizer. This would
probably demand more thrust (at first), but the more important issue
is the amount of fuel.
Mike Miller
Jon Berndt
> 3. How much bigger (more thrust) would SS1 have to have to achieve orbit ?
More (longer/bigger) = more fuel = larger structure = more weight = more
fuel = etc.
;-)
You can look at it several ways, but one interesting comparison is this:
SS1 max speed = about 2500 fps (IIRC)
Orbital speed = about 25000 fps
You need ten times more speed, but that's not the whole story either. You
have to impart a bunch of energy to a mass to get it into orbit. You can
sort of approximate this with the sum of the kinetic and potential energy
per pound of mass for a low orbit. I can't recall what the potential energy
is for orbits (I would have thought it's simply mgh, but something tells me
that's _almost_ right) but kinetic energy is much greater at 0.5mv^2. The
kinetic energy scales with the square of velocity. IOW, you need to impart
100 times more energy to the vehicle _per_pound_ to get it into orbit
(actually more, because you have to make up losses due to drag). Remember,
too, that they have to carry fuel onboard to perform a deorbit manuever
later on.
Maybe the answer is to fit a rocket engine or two to WhiteKnight. If White
Knight could carry SS1 to 60 miles and Mach 22 then maybe there's a chance
..
;-)
Scott Lowther
>
> In article <OJQBc.157831$Ly.127326@attbi_s01>,
> Scott Moore <sam...@moorecad.com> wrote:
> >1. assuming the next "big prize" would be an orbital vehicle, what is the
> >lowest altitude an object can be orbited at, if only for a circuit or so ?
>
> At about 150km it's marginally possible. 200km is more comfortable.
Of course, Rutan has already done a single orbit vehicle, at a far lower
altitude...
--
Scott Lowther, Engineer
Remove the obvious (capitalized) anti-spam
gibberish from the reply-to e-mail address
EAC
> If you can forgive a dumb space question or two:
>
> 1. assuming the next "big prize" would be an orbital vehicle,
> what is the lowest altitude an object can be orbited at,
> if only for a circuit or so ?
Vostok's orbit is around 200 Km.
And according to this calculation page below:
http://liftoff.msfc.nasa.gov/academy/rocket_sci/orbmech/vel_calc.html
http://liftoff.msfc.nasa.gov/Scripts/Orb_vel.pl?Radius=184%2C999999999
http://liftoff.msfc.nasa.gov/Scripts/Orb_vel.pl?Radius=185
Anything below 185 Km is not stable and to orbit at 185 km it took the
orbital velocity of 28.044 kilometers / hour.
> 2. If SS1 wanted to go somewhere instead of straight up,
> would it be able to, say, cross the United States at several mach,
> above the atmosphere ?
Possible, if it was heavily redesigned. But then again, when that
happened, it's much better to called it Space Ship Two, or just plain
Super Sonic Transport.
> 3. How much bigger (more thrust) would SS1 have to have to achieve orbit ?
It's not only thrust is needed, but also Total Impulse.
I think that the whole Total Impulse of the R-7 that tool Vostok to
orbit is 752,15392 millions Newton-seconds , while Space Ship One's
Total Impulse is around 0,78% of that.
If things stay the way they're, White Knight would do no good, it's
better to stick Space Ship One on top of the R-7. Though there's still
the problem of slowing down from orbital velocity, can Space Ship One
reduce it speed safely from the orbital velocity of around 28.000 Km
/hour at the orbit of around 200 km?
> Thanks.
Joe Pfeiffer
> Henry Spencer wrote:
> >
> > In article <OJQBc.157831$Ly.127326@attbi_s01>,
> > Scott Moore <sam...@moorecad.com> wrote:
> > >1. assuming the next "big prize" would be an orbital vehicle, what is the
> > >lowest altitude an object can be orbited at, if only for a circuit or so ?
> >
> > At about 150km it's marginally possible. 200km is more comfortable.
>
> Of course, Rutan has already done a single orbit vehicle, at a far lower
> altitude...
Not using *anybody's* reasonable definition of "orbit."
--
Joseph J. Pfeiffer, Jr., Ph.D. Phone -- (505) 646-1605
Department of Computer Science FAX -- (505) 646-1002
New Mexico State University http://www.cs.nmsu.edu/~pfeiffer
Southwestern NM Regional Science and Engr Fair: http://www.nmsu.edu/~scifair
Scott Lowther
>
> Scott Lowther <scottlowth...@ix.netcomARGH.com.retro.com> writes:
>
> > Henry Spencer wrote:
> > >
> > > In article <OJQBc.157831$Ly.127326@attbi_s01>,
> > > Scott Moore <sam...@moorecad.com> wrote:
> > > >1. assuming the next "big prize" would be an orbital vehicle, what is the
> > > >lowest altitude an object can be orbited at, if only for a circuit or so ?
> > >
> > > At about 150km it's marginally possible. 200km is more comfortable.
> >
> > Of course, Rutan has already done a single orbit vehicle, at a far lower
> > altitude...
>
> Not using *anybody's* reasonable definition of "orbit."
Pfah. Once all the way around the planet without touching down. Close
enough for government work...
sm...@yahoo.com
> Scott Lowther <scottlowth...@ix.netcomARGH.com.retro.com> writes:
>
[...]
> > Of course, Rutan has already done a single orbit vehicle, at a far lower
> > altitude...
>
> Not using *anybody's* reasonable definition of "orbit."
>From Webster's online dictionary:
Main Entry: 2orbit
Function: noun
[...]
b : a circular path
Main Entry: 3orbit
Function: verb
[...]
intransitive senses : to travel in circles
Mike Jones
Yeah, I think it is more like 8 or 9 times faster needed for orbit
than SS1 achieved, but it hardly matters.
In reality, probably 100 times more power is needed for something of
SS1's mass to get into orbit - obviously, putting in 100 times more
fuel won't do that, as that would increase the weight dramatically.
As it is, using SS1's engines (A nitrous-oxide HBTP hybrid booster)
can't achieve anything like a high enough ISP (power/weight ratio,
effectively) to get anywhere close to orbit - a complete re-design
would be needed.
>From what I've read of Rutan's comments, he intends to do it in stages
- first making a 6 person craft to go to 150 Km and maybe double the
peak velocity, and so on. Whether he will be able to achieve orbit
without massive funding remains to be seen.
The challenges of getting to orbit compared with leaving the
atmosphere is much like comparing the challenge of getting off the
ground in the first place to leaving the atmosphere. Ie, it's huge.
Ian Stirling
> Scott Moore <sam...@moorecad.com> wrote in message news:<OJQBc.157831$Ly.127326@attbi_s01>...
>> If you can forgive a dumb space question or two:
>>
>> 1. assuming the next "big prize" would be an orbital vehicle, what is the lowest
>> altitude an object can be orbited at, if only for a circuit or so ?
>
> At 90-100 miles, drag should be low enough to complete one orbit.
It depends somewhat on the density of the object.
If it's really low (a balloon) then it'll need to orbit much higher than
if it's a solid 100m long bar of tungsten.
At 100Km, and at orbital speeds, the pressure exerted by the atmosphere
on the vehicle is around 2Kg force/square meter.
This will cause a balloon to slow at around 20000m/s (it'll effectively come
to a stop in half a second and drift down) but the bar of tungsten by only
a billionth of a the same amount, and it'd take some 15 years to slow
as much.
(though as it slows down, it drops, so it'll come in faster, maybe a
few months.)
Hephaestus
>
> No. The artillery rule of thumb is that maximum horizontal range is twice
> the altitude reached when fired straight up, which would give SS1 maximum
> range of only a couple of hundred kilometers.
It is useful to note that this makes SS1 roughly comparable in performance
to a V2 rocket.
This might help people comprehend how big a step it is from SS1 to an orbital
ship. The V2 was first launched in 1944, but an orbital launch vehicle with
a payload of similar magnitude didn't fly until over 20 years later. And
it didn't have to come back ...
Tony Rusi
energy to get to LEO. That would be roughly 20 times. Any vehicle that
makes the use of a mothership a waste of time, as a staged rocket
traverses the first 60k in less than a minute and a half. Flying
around for an hour will not lead to a practical commercial space
vehicle. Wings on such a vehicle are really more of a liability than
any type of advantage, as we have witnessed with the shuttle. The only
reason the space shuttle had wings is because some aging USAF type
demanded it, and no one wanted to argue. Thank God Elon Musk found Tom
Mueller and is leading America's commercial space future into LEO with
a no nonsense 3 stage rocket design.
Don't get me wrong. I think Rutan is a genius. I wish Paul Allen would
give him a billion to build a moon-mars transportation infrastructure.
It will probably look a lot like the Seadragon concept. The SS1 is
just a first step back towards rationality. Truax outlined a rational
approach to low cost access to space in Aerospace America a few years
back. It should be required reading for every aerospace engineer.
Joann Evans
>
> I have heard aerospace engineers say that SS1 would need 95% more
> energy to get to LEO. That would be roughly 20 times. Any vehicle that
> makes the use of a mothership a waste of time, as a staged rocket
> traverses the first 60k in less than a minute and a half. Flying
> around for an hour will not lead to a practical commercial space
> vehicle. Wings on such a vehicle are really more of a liability than
> any type of advantage, as we have witnessed with the shuttle. The only
> reason the space shuttle had wings is because some aging USAF type
> demanded it, and no one wanted to argue.
No, it was the then-reasonable requirement to launch south from
Vandenberg, and return to that same site after one orbit, and Earth has
turned quite a bit in the meantime. Delta wings were necessary to get
the needed cross-range. Otherwise, a straight-wing design might've been
used...
...but there *would* have been wings of some sort, regardless.
--
You know what to remove, to reply....
Allen Meece
The performance may be comparable to a V-2 but the function couldn't be more
different! This is the pathfinder to space for the common man.
Anolther way to view the SS1 achievement: Someone has said that getting to
orbit takes 30 times more energy than getting to space vertically.
But after all's said and done, the achievement of SS1 was to show the world
that space ain't that far away nor that hard to do!!! It's major effect is to
build confidence.
Thanks, Paul Allen, for paying for the project. You're the first billionaire
I like.
^
//^\\
~~~ near space elevator ~~~~
~~~members.aol.com/beanstalkr/~~~
Allen Meece
one is so much harder. I don't get why there are so many pessimists out there.
Something to do with hoplessness.
Orbit is easy. There, that wasn't so hard.
<<The challenges of getting to orbit compared with leaving the
atmosphere is much like comparing the challenge of getting off the
ground in the first place to leaving the atmosphere. Ie, it's huge>>
Allen Meece
on the vehicle is around 2Kg force/square meter.
This will cause a balloon to slow at around 20000m/s (it'll effectively come
to a stop in half a second and drift down) >>
orbit. Balloons can be built streamlined to have lift and they can assume an
angle of attack that will be forced upward by the high speed slipstream.
I think they'll want to avoid all air molecules and orbit higher than 200
km altitude though.
Ian Stirling
> Ian Stirling wrote:
>> At 100Km, and at orbital speeds, the pressure exerted by the atmosphere
>> on the vehicle is around 2Kg force/square meter.
>> This will cause a balloon to slow at around 20000m/s (it'll effectively come
>> to a stop in half a second and drift down)
As a further note, to increase the atmospheric density by a million fold, you
need to drop down from 100Km to around 22Km.
This means that to get an orbit similar to one at 100Km at 22Km, you need
a million times the density per unit area.
I was assuming that the average sectional density was around a gram
a square meter for the balloon, and there was no lift.
> JP Aerospace may not agree with this pessimistic view of balloon behavior in
> orbit. Balloons can be built streamlined to have lift and they can assume an
> angle of attack that will be forced upward by the high speed slipstream.
A lot of people think that JP Aerospace are on really, really good drugs,
to believe this.
> I think they'll want to avoid all air molecules and orbit higher than 200
> km altitude though.
There is significant atmosphere (for very low density satellites)
to be significant at 200Km.
Allen Meece
>> At 100Km, and at orbital speeds, the pressure exerted by the atmosphere
>> on the vehicle is around 2Kg force/square meter.
come
>> to a stop in half a second and drift down) >>>
The beauty of JPA's orbital balloon plan is that there is no need to
raapidly accelerate to orb speed. It's about converting and efficiently using
solar energy to operate an electric drive. Thus, orb speed doesn't *have* to
rapidly occur as it does in a rocket shot. They're talking about taking a week
to reach orbit.
John Schilling
>I have heard aerospace engineers say that SS1 would need 95% more
>energy to get to LEO. That would be roughly 20 times. Any vehicle that
>makes the use of a mothership a waste of time, as a staged rocket
>traverses the first 60k in less than a minute and a half.
The purpose of the "mother ship" is not to save the spacecraft the
trouble of crossing the first 60k feet. The purpose of the "mother
ship" is to save the spacecraft the trouble of carrying to space
the very specialized hardware necessary to support itself on and
lift itself off the ground (which may or may not be substantial,
depending on detailed design decisions for which there is no obvious
best answer), and to allow it to use rocket engines optimized for
high-altitude operation (which are substantially more efficient than
rocket engines designed for sea-level operation, but which would
tear themselves apart if lit off at or near sea level).
>Flying around for an hour will not lead to a practical commercial space
>vehicle.
Flying around for an hour is essentially irrelevant to whether or not
a space vehicle is commercially practical.
>Wings on such a vehicle are really more of a liability than any type of
>advantage, as we have witnessed with the shuttle.
As we have witnessed *on the shuttle*, wings are *essential* to such a
vehicle. Space shuttles with wings have conducted many space flights
with >98% reliability. A space shuttle stripped of its wings would
fall out of the sky and make a smoking hole in the landscape at the
end of its first flight.
Perhaps you meant to say, "as we have witnessed by comparing the shuttle
with the wingless vehicle I imagine should have been built in the shuttle's
place". But first off, that's something only you have witnessed. Second,
the wingless vehicle you imagine should have been built in the shuttle's
place, will still need *something* to keep it from falling out of the
sky and making a smoking hole in the landscape. And people have put a
lot of effort into looking at all the systems for handling that part of
the mission, including but not limited to wings, without finding a clear
and unambiguous answer as to which is best.
(hint: they *all* involve carrying a lot of dead weight to orbit, on the
order of 10% of the vehicle's landing mass)
>The only reason the space shuttle had wings is because some aging USAF type
>demanded it, and no one wanted to argue.
I think you're selectively remembering history here. The USAF, in the
form of officers who were not aging any faster than the rest of us, demanded
that the wings be deltas of relatively high planform area. The shuttle's
civilian designers had *already* decided on wings, albeit rather stubbier
ones, because they felt that they were as good a way as any of keeping the
thing from falling out of the sky and making a smoking hole in the ground
at the end of its flight.
>Thank God Elon Musk found Tom Mueller and is leading America's commercial
>space future into LEO with a no nonsense 3 stage rocket design.
Neither Elon Musk nor Tom Mueller invented the three-stage rocket.
>Don't get me wrong. I think Rutan is a genius. I wish Paul Allen would
>give him a billion to build a moon-mars transportation infrastructure.
>It will probably look a lot like the Seadragon concept. The SS1 is
>just a first step back towards rationality. Truax outlined a rational
>approach to low cost access to space in Aerospace America a few years
>back. It should be required reading for every aerospace engineer.
Nor did Truax.
And we get more than enough True Believers here, sure that they and their
designated rocket-building heroes have the One True Way to Space, ready
to spark a Holy War with all the unbelievers who still cling to their
winged/VTVL/hydrogen/airbreathing/kerosine/hydrogen/airbreathing/rocket/
SSTO/TSTO/BDB concepts.
And they're all wrong. There *is* no One True Way, but a diverse assortment
of concepts whose relative merit is very sensitive to details impossible
to pin down in any absolute sense at this time.
Required reading for every aerospace engineer? That's a long list, but
in your case we'll start with Mitchell Burnside-Clapp's "The Palpable
Superiority of Horizontal Landing", from right here in this newsgroup
a few years back.
--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
*schi...@spock.usc.edu * for success" *
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H MURDOCH
>>space future into LEO with a no nonsense 3 stage rocket design.
>
>Neither Elon Musk nor Tom Mueller invented the three-stage rocket.
But perhaps they did invent the 2 stage rocket ;-) Although my skill with
arithmetic may be suspect, I count roughly 2 (two) stages for both the Falcon
and the Falcon V launchers as shown on SpaceX's website. In fact they make a
point of hoping to increase reliability by having the minimum number of staging
events practically possible.
Re Rutan and wings - lets not forget that SS1 is built for a limited goal, and
can fairly easily meet that goal and still achieve horizontal landings on a
runway with wings. Easy on the passengers or pilot and machinery vs parachute
touchdowns, and very easy to turn the vehicle around with minimal servicing
etc.
Re other methods of landing - having watched a few sucessful DC-X landings
using rocket power at White Sands, I would nonetheless feel more comfortable as
a passenger gliding down to a runway, than anxiously waiting till the last few
seconds before becoming part of a crater in the ground for the rocket engines
to throttle up.
Granted, there are a lot of tradeoffs that can be argued for or against all the
schemes for getting to and back from space. But I tend to agree that no one
architecture has yet shown itself to be the *one* best way to go.
But the fact that a civilian in a privately funded craft got into space I think
will in the long run matter far more than whether his vehicle had wings or
parachutes or airbags or rotors.
Hank M.
Joann Evans
> Re other methods of landing - having watched a few sucessful DC-X landings
> using rocket power at White Sands, I would nonetheless feel more comfortable as
> a passenger gliding down to a runway, than anxiously waiting till the last few
> seconds before becoming part of a crater in the ground for the rocket engines
> to throttle up.
Your point's taken, however, pre-shuttle crews took normal parachute
deployment for granted (despite Soyuz-1), and aircraft passengers seem
to take normal landing gear extension for granted. (That failure is what
destroyed DC-X in the end) Given time, and enough successful, routine
altitude start of engines, people will get used to it.
And if there's to be comercial Lunar flight, well, they simply must.
> Granted, there are a lot of tradeoffs that can be argued for or against all the
> schemes for getting to and back from space. But I tend to agree that no one
> architecture has yet shown itself to be the *one* best way to go.
Agreed here, though. Even hypersonic air-breathers to orbit will have
a place but, I suspect it will be a specialized, mostly military niche.
Not the way most of us will get to LEO.
> But the fact that a civilian in a privately funded craft got into space I think
> will in the long run matter far more than whether his vehicle had wings or
> parachutes or airbags or rotors.
>
> Hank M.
Earl Colby Pottinger
> And we get more than enough True Believers here, sure that they and their
> designated rocket-building heroes have the One True Way to Space, ready
> to spark a Holy War with all the unbelievers who still cling to their
> winged/VTVL/hydrogen/airbreathing/kerosine/hydrogen/airbreathing/rocket/
> SSTO/TSTO/BDB concepts.
>
> And they're all wrong. There *is* no One True Way, but a diverse
assortment
> of concepts whose relative merit is very sensitive to details impossible
> to pin down in any absolute sense at this time.
Worse, there probably are 'One True Way's for certain markets, but outside of
that market that way of doing things is at a major disavantage that promises
to bankrupt anyone trying to push that 'One True Way'.
Earl Colby Pottinger
--
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SerialTransfer 3.0, RAMDISK, BoatBuilding, DIY TabletPC. What happened to
the time? http://webhome.idirect.com/~earlcp
Ian Stirling
And lots of people think they are smoking really good drugs.
A week to reach orbit implies hypersonic lift over a hundred times
better than anyone has ever gotten.
Iain McClatchie
Ian> A week to reach orbit implies hypersonic lift over a hundred times
Ian> better than anyone has ever gotten.
In particular, buoyancy for lift seems troublesome. Buoyancy (for a
zero-mass gas) is the difference in pressure between the top and bottom
of the balloon, so there has to be pressure on the bottom of the balloon
for it to happen. Surely the dynamic pressure on the side of the
balloon will equal the static pressure on the bottom of the balloon at
relatively low speeds, at which point the balloon's horizontal motion
will decrease at 1G.
Hmm... Pd = 0.5*p*u^2. PsV = nRT, so Ps = T*(nR/V)
where
Pd is dynamic pressure
Ps is static pressure
p is density
u is velocity
p = nW/V
where
W is average molecular weight
Pd = Ps when
0.5*p*u^2 = T*(nR/V)
0.5*nW/V*u^2 = T*(nR/V)
u^2 = 2RT/W
At W = 29 g/mol
T = 180 K
R = 8.3 J/mol-K
u^2 = 103 J/g
u = 103 km/s
Hmm... that looks well above orbital speed. Did I screw up
the math? This pretty much contradicts the intuition that
balloons go where the wind blows them.
Iain McClatchie
The answer is 320 m/s, not 103,000 (m/s)^2. D'oh.
Andres del Pozo
> >Flying around for an hour will not lead to a practical commercial space
> >vehicle.
>
> Flying around for an hour is essentially irrelevant to whether or not
> a space vehicle is commercially practical.
In fact for passenger service it would probably be an advantage.
Nowadays a trip to the space station takes more than two days because
there are very few launch windows that allow to reach ISS faster.
>From a static spaceport the ground track of ISS is near enough only a
couple of times each day. Most days you need a quite long period in
orbit to achieve the correct phasing for docking.
A rocket launched from a plane after 5 hours of flight could select
ground tracks in a circle with a diameter of about 10000Km. It is much
more probable that one of those launch windows could allow to dock in
less time. Probably it could be possible to reduce the time in orbit
before docking from 2 days to less than a day.
Andrés.