Aerobraking on the way up
Alain Fournier
A first step towards building a fully reusable rocket would be to have a reusable first stage. You would want to
minimize maintenance cost on that first stage. Preferably it would be a Buck-Rogers type of first stage, you use it, it
comes back, you fill it up, and you use it again. You want it to be inexpensive to use, so you don't want to need an
army of technicians to work on it between each flight.
I'm trying to figure out what performance such a first stage should perform. If the first stage brings the second stage
to half of orbital speed (4 km/s) it will need a heat shield and a long fly back, that might not be compatible with
inexpensive, rugged and current technological levels. On the other hand, if it only accelerates straight up to 5 km, you
won't need a heat shield and fly back will be easy, but it doesn't provide much of a boost.
So, what should be the task of the first stage? I'm trying to figure out the maximum performance it could have, without
a significant heat shield and with line of sight fly back (never goes over the horizon). An idea I had while thinking
about that is to aerobrake on the way up. Let's say you have first stage separation at an altitude of 80 km. Because of
momentum, the first stage will continue to go up and further away. You might want to turn the first stage side ways, so
it starts decelerating. Then as it goes up lower atmospheric pressure stops the aerobraking, lets the first stage cool
down for a minute or two before reentery at a lower velocity than if it had not aerobraked on the way up.
Does it make any sense to aerobrake on the way up? Probably not. The problem is that your highest speed is at the
densest part of the atmosphere so this is probably not a good way to minimize the need for thermal protection. But
still, I can't think of a strong argument showing that there isn't some altitude where it would make sense to start
aerobraking on the way up.
Does anyone know if this kind of thing has ever been studied before? Or does anyone know of an argument that would show
that aerobraking on the way up does/doesn't make sense?
Alain Fournier
Derek Lyons
>A first step towards building a fully reusable rocket would be
>to have a reusable first stage. You would want to minimize
>maintenance cost on that first stage. Preferably it would be a
>Buck-Rogers type of first stage, you use it, it comes back, you
>fill it up, and you use it again. You want it to be inexpensive
>to use, so you don't want to need an army of technicians to work
>on it between each flight.
Reliable, cheap, third generation.
Pick two.
D.
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Oct 5th, 2004 JDL
Pat Flannery
Alain Fournier wrote:
>
>
> Does it make any sense to aerobrake on the way up?
I would think that would make a _lot_ of sense; as soon as stage one
separates, anything you can do to start slowing it down immediately
rather than having it coast higher and the start falling ballisticlly
back into the atmosphere makes a lot of sense in regards to both thermal
and aerodynamic stress on its way back down.
It also means that it will descend back into the atmosphere closer to
its launch point, making recovery easier in either the "parachute into
the sea" or "glide-land to the launch point" scenarios.
Since there will probably still be atmosphere of some density around it
when it separates from the second stage, using air drag in some way to
slow it down probably is lighter to do than using some sort of
retro-rockets on it.
> Probably not. The problem is that your highest speed is at the densest
> part of the atmosphere so this is probably not a good way to minimize
> the need for thermal protection. But still, I can't think of a strong
> argument showing that there isn't some altitude where it would make
> sense to start aerobraking on the way up.
>
> Does anyone know if this kind of thing has ever been studied before?
> Or does anyone know of an argument that would show that aerobraking on
> the way up does/doesn't make sense?
Back when NASA was considering a recoverable version of the Saturn V
first stage, it was going to use four enlarged fins around its base that
were going to open split airbrakes as it began to descend; to both cut
its velocity and get it going top-end first toward the water.
You _really_ want to see a first stage decelerate itself via aerobraking
after separation, go back the the von Braun "Ferry Rocket" from Colliers
Magazine in the 1950's... that thing had a large annular steel-mesh
parachute come out around its base after it separated, as did the
rocket's second stage also.
Another great webpage from "Project Rho":
http://www.projectrho.com/rocket/rocket3ai.html
Boy, could that Chesley Bonestell paint.
After the EVA video from Apollo 11 started coming in, von Braun leaned
over to Bonestell and said: "Don't worry Chesley... you were right...
the Moon was wrong..." :-D
Pat
Pat Flannery
Derek Lyons wrote:
>
> Reliable, cheap, third generation.
>
> Pick two.
>
You might want to rephrase that as "reliable/cheap/wasteful...or...
recoverable/reusable/ technologically sweet... pick one of those two
concepts", because I get a sneaking suspicion that they both come out
costing around the same when all is said and done, except that the
second one is going to cost several billion dollars more to develop than
the first (existing) one.
Pat
Day Brown
it makes good engineering sense to delve into, wont get the political
support to get off the ground. Never mind orbit.
Eco freaks will be screaming about the air pollution should chemical
rockets ever be used in enough numbers to do anything substantial in space.
The only way to do it now, would be to build a nuke at the base of some
equatorial mountain, and use it to power a mag lev up the side of that
slope to get so high above the atmosphere that there wont be any video
of the smoke trail when the 2nd stage boosters come on.
While the upfront costs would be horrendous, the damn thing would be
able to send up a first stage booster every 20 minutes like a bus. If it
didnt have the 2nd and 3rd stage, it could fly suborbital to deliver
passengers and freight at hypersonic speed, with zero gravity for
several minutes, which'd pay off in tourist tickets.
Course, in the meantime, if they develop nuclear fusion, then anybody
could launch from anywhere to go anywhere.
Jorge R. Frank
>
> A first step towards building a fully reusable rocket would be to have a
> reusable first stage. You would want to minimize maintenance cost on
> that first stage. Preferably it would be a Buck-Rogers type of first
> stage, you use it, it comes back, you fill it up, and you use it again.
> You want it to be inexpensive to use, so you don't want to need an army
> of technicians to work on it between each flight.
>
> I'm trying to figure out what performance such a first stage should
> perform. If the first stage brings the second stage to half of orbital
> speed (4 km/s) it will need a heat shield and a long fly back, that
> might not be compatible with inexpensive, rugged and current
> technological levels. On the other hand, if it only accelerates straight
> up to 5 km, you won't need a heat shield and fly back will be easy, but
> it doesn't provide much of a boost.
>
> So, what should be the task of the first stage?
As with expendable first stages, it should be designed to get the second
stage above most of the atmosphere, allowing the second stage design to
be optimized for vacuum and the first stage for atmospheric flight.
That implies a staging altitude/velocity not too different from current
two-stage rockets: ~40-50 km and ~1-1.5 km/s.
The TPS requirements for such a stage are not onerous even if you don't
make maximum use of drag (I won't call it "aerobraking"; that's not
proper usage of the term) on the way up.
Dr J R Stockton
dakotatelephone>, Sun, 31 May 2009 02:28:16, Pat Flannery
<fla...@daktel.com> posted:
>Alain Fournier wrote:
>> Does it make any sense to aerobrake on the way up?
>I would think that would make a _lot_ of sense; as soon as stage one
>separates, anything you can do to start slowing it down immediately
>rather than having it coast higher and the start falling ballisticlly
>back into the atmosphere makes a lot of sense in regards to both
>thermal and aerodynamic stress on its way back down.
If you look into the height at stage separation, I suspect that you will
find that there is so little atmosphere up there that the effect will be
very small. A small effect is of some use; but not if it carries a mass
penalty.
--
(c) John Stockton, near London. *@merlyn.demon.co.uk/?.?.Stockton@physics.org
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Alain Fournier
> In sci.space.tech message <xpudneOEJerJir_X...@posted.north
> dakotatelephone>, Sun, 31 May 2009 02:28:16, Pat Flannery
> <fla...@daktel.com> posted:
>
>>Alain Fournier wrote:
>
>>>Does it make any sense to aerobrake on the way up?
>
>>I would think that would make a _lot_ of sense; as soon as stage one
>>separates, anything you can do to start slowing it down immediately
>>rather than having it coast higher and the start falling ballisticlly
>>back into the atmosphere makes a lot of sense in regards to both
>>thermal and aerodynamic stress on its way back down.
>
> If you look into the height at stage separation, I suspect that you will
> find that there is so little atmosphere up there that the effect will be
> very small. A small effect is of some use; but not if it carries a mass
> penalty.
You choose the height at stage separation, and you can choose it in such a
way that there is enough atmosphere. If you want your first stage to fly back
to the launch site, stage separation shouldn't be to late.
Alain Fournier
Pat Flannery
Dr J R Stockton wrote:
> If you look into the height at stage separation, I suspect that you will
> find that there is so little atmosphere up there that the effect will be
> very small. A small effect is of some use; but not if it carries a mass
> penalty.
>
I checked up on the Saturn V, and stage one separated at between 38-42
miles (sources differ), so that's 200,640 to 221,760 feet. That means
the air will be very thin indeed, but there should be some small effect,
as can be seen by the fact that the rocket exhaust was still being swept
back to some degree at staging. Speed is also important here, as though
the atmospheric pressure may have been very low, the stage was passing
through it at 5,352 mph at shutdown.
As you say, you have to weigh off the advantages of trying to slow the
stage down immediately after separation to bring it down close to the
launch point or prevent it building up speed as it begins to descend
(which will result in severe structural stress) versus the weight of the
system to do that. One simple and lightweight way of doing this would be
turning the stage side-on to its flightpath so as to maximize the air
drag on it.
IIRC, the Saturn V first stage broke up as it fell back toward the Earth
from aerodynamic stress.
Pat