Reasonable Minimal Size for a 2-Man Capsule?
Jonathan Goff
Just wanted to pop in for a second to get people's opinions on a
technical question. I've been doing some high-level number crunching
for lunar missions in my spare time again, and was trying to come up
with a reasonable size for a 2-man crew capsule.
Basically, this crew capsule wouldn't be performing any of the major
burns, just providing enough propulsion capabilities to handle post-TEI
mid course corrections and reentry. It would need to have (obviously)
a heat shield and a landing system (parachutes or otherwise). The
capsule would need to support the two-man crew for up to 8 days (ie a
1-2 day lunar stay), and include a hatch, and room for two spacesuits.
The idea would be to have it just roomy enough to be workable for 8
days, but otherwise as small as reasonably possible.
Anyhow, what do you guys think a reasonable weight target for such a
design would be? The 3-man Apollo CM was about 5800kg, and the 2-man
Gemini was about 3800kg. t/Space was talking about 4000kg for a 4-man
reusable orbital capsule, and SpaceX is looking at 7 people for less
than 9000kg including the escape tower. I know that George Herbert has
suggested that a 1-person capsule could be doable in the 300-400kg
range, though that seems a bit sporty.
I guess I'm having a hard time coming up with a realistic number
because most of the previous manned capsules were done with 60s era
manufacturing, electronics, and power systems. And most modern designs
have different design goals in mind.
Anyone have any thoughts? Henry? Derek? Rand? John?
~Jon
Rand Simberg
Goff" <jon...@gmail.com> made the phosphor on my monitor glow in such
a way as to indicate that:
>Anyhow, what do you guys think a reasonable weight target for such a
>design would be? The 3-man Apollo CM was about 5800kg, and the 2-man
>Gemini was about 3800kg. t/Space was talking about 4000kg for a 4-man
>reusable orbital capsule, and SpaceX is looking at 7 people for less
>than 9000kg including the escape tower. I know that George Herbert has
>suggested that a 1-person capsule could be doable in the 300-400kg
>range, though that seems a bit sporty.
>
>I guess I'm having a hard time coming up with a realistic number
>because most of the previous manned capsules were done with 60s era
>manufacturing, electronics, and power systems. And most modern designs
>have different design goals in mind.
>
>Anyone have any thoughts? Henry? Derek? Rand? John?
Sorry, I'm not a weights guy, but I'd think that Henry would have a
good guesstimate. It might help if you provided a link to the
relevant post for more info.
Jonathan Goff
> Sorry, I'm not a weights guy, but I'd think that Henry would have a
> good guesstimate. It might help if you provided a link to the
> relevant post for more info.
Good point. Here's the link to the relevant post on my blog:
http://www.selenianboondocks.com/2006/12/2-man-eelv-based-mission-numbers.html
The spreadsheets that go with it are at:
http://spreadsheets.google.com/pub?key=pD9i_cIb_0jC2LlfgSOQJAQ
Come to think of it, I have a few other people I ought to ping with the
question directly.
~Jon
Derek Lyons
>Anyone have any thoughts? Henry? Derek? Rand? John?
Henry would be your weights guy. (And George.) The rest of us are
better on the analysis/philosophy/has your wee one been keeping you up
too late to think this was a good idea? side of things.
D.
--
Touch-twice life. Eat. Drink. Laugh.
-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL
Jonathan Goff
> Henry would be your weights guy. (And George.) The rest of us are
> better on the analysis/philosophy/has your wee one been keeping you up
> too late to think this was a good idea? side of things.
Well, do you have any opinions about my analysis/philosophy for this
architecture concept?
~Jon
Alex Terrell
http://www.astronautix.com/craft/cev.htm
It implies better way is to have your landing capsule as small as
possible - just big enough for two crew. The galley, toilet, motors etc
are housed in a separate unit which detaches and burns up, so the heat
shield doesn't need to support these.
Dr J R Stockton
<1165055513....@j72g2000cwa.googlegroups.com>, Sat, 2 Dec 2006
02:31:53, Alex Terrell <alext...@yahoo.com> wrote:
>Jonathan Goff wrote:
>> Just wanted to pop in for a second to get people's opinions on a
>> technical question. I've been doing some high-level number crunching
>> for lunar missions in my spare time again, and was trying to come up
>> with a reasonable size for a 2-man crew capsule.
>Take a look at this article
>http://www.astronautix.com/craft/cev.htm
>
>It implies better way is to have your landing capsule as small as
>possible - just big enough for two crew. The galley, toilet, motors etc
>are housed in a separate unit which detaches and burns up, so the heat
>shield doesn't need to support these.
Alternatively:
Note that a crew couch for zero g does not need to fit, and for lunar
takeoff it needs only a light liner.
At Earth approach the crew don their suits, seal them, and lie in their
couches, using liners that fit their suits. They close a
nominally-airtight but vented cover over each couch. When about to
enter atmosphere, the couches are ejected and have or deploy enough
aerodynamics to drift them away from the abandoned capsule. The
heat-shields under the couches protect and slow them; the couches may
deploy drogue or full parachutes, and the occupant may or may not land
independently with a personal chute.
Or as above but using a two-pit couch.
--
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Web <URL:http://www.merlyn.demon.co.uk/> - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.
Henry Spencer
Jonathan Goff <jon...@gmail.com> wrote:
>...would need to support the two-man crew for up to 8 days (ie a
>1-2 day lunar stay), and include a hatch, and room for two spacesuits.
>The idea would be to have it just roomy enough to be workable for 8
>days, but otherwise as small as reasonably possible.
With one major exception (see below), volume and mass are pretty much two
separate issues. The mass penalty of making the thing roomier and hence
easier to live in is quite small. Even the heatshield mass scales much
more strongly with capsule mass than with capsule volume, because a
fluffier capsule sees a gentler reentry environment.
>...The 3-man Apollo CM was about 5800kg, and the 2-man Gemini
>was about 3800kg. t/Space was talking about 4000kg for a 4-man reusable
>orbital capsule, and SpaceX is looking at 7 people for less than 9000kg
>including the escape tower. I know that George Herbert has suggested
>that a 1-person capsule could be doable in the 300-400kg range...
I once did a back-of-the-envelope estimate suggesting that you could do a
3-man capsule for around 1000kg (including occupants). But that was an
aggressive and severely Spartan design, basically a 3-man Mercury -- no
maneuverability except retrofire, short in-space life, no amenities --
meant as a crew ferry to a space station which had its own tug to bring
you in (and with the launch-window issues of first-day rendezvous sort of
glossed over...). And I never carried the details far enough to decide
whether it was really workable.
Hempsell's "Excalibur" is a reasonable example of a fairly aggressive
modern design, 4 men for 10 days in 10100kg... and about half that mass is
fuel, giving it 2km/s of delta-V, so it's more like 5000kg if you don't
require much maneuverability.
One rule of thumb I've long held is that since giving each guy his own
Mercury capsule takes about 1500kg/man, any vehicle heavier than that is
inexcusably overweight unless it's doing something rather more ambitious.
(Gemini and Apollo are not far above that, and probably get a passing mark
due to greater capabilities. NASA's new barge is another story.)
>I guess I'm having a hard time coming up with a realistic number
>because most of the previous manned capsules were done with 60s era
>manufacturing, electronics, and power systems...
You can safely assume that the electronics weigh essentially nothing, and
power systems will be a lot lighter because they have to do much less.
One snag for a *lunar* capsule is radiation shielding: of some
significance because of deep-space background radiation, somewhat more
important due to the possibility of giant flares, and utterly vital for
passage through the Van Allen belts. This is where having a lot of bulky
heavy equipment and an overbuilt heatshield win -- Apollo had about
8g/cm^2 (aluminum equivalent) of protection even with no mass explicitly
budgeted for shielding. And this is one place where volume matters, or
more precisely, surface area matters.
Modeling a two-man capsule crudely as a 2m-dia hemisphere, it has about
10m^2 of wall area including the base, or around 800kg at 8g/cm^2. Now,
that's a conservative number because aluminum is not actually the best
shielding; something with a lot of hydrogen in it will be better. If we
assume that the heatshield and related structure are enough shielding for
the base (ca. 3.5m^2), and that elsewhere the walls and other structure
contribute 2g/cm^2, and that added shielding is high-density polyethylene
(perhaps twice as good as aluminum), that's maybe 200kg of shielding,
which isn't too bad. Significant, but not a showstopper.
Anyway, given that and the longer in-space life and a high-energy reentry,
you definitely can't be as aggressive as that lightweight design sketch of
mine. But you really shouldn't need as much mass as a Gemini. Take the
geometric mean of the two and call it 2000kg, as a first guess, given firm
design discipline and no severe externally-imposed requirements (e.g., a
demand for much more radiation shielding than Apollo had).
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. | he...@spsystems.net
Henry Spencer
Derek Lyons <fair...@gmail.com> wrote:
>>Anyone have any thoughts? Henry? Derek? Rand? John?
>
>Henry would be your weights guy. (And George.)
George would actually be your clear choice on this one, because he's
certainly looked into it in greater depth than I have. But I've ventured
some quick first guesses in another posting...
Derek Lyons
It's great if you haven't any ambitions beyond multiple short trips -
beyond that I don't see the point. (I also detect the engineers
fascination with weight and cost - but nowhere is the science
capabilities adressed.)
Oren
...
> Modeling a two-man capsule crudely as a 2m-dia hemisphere, it has about
> 10m^2 of wall area including the base, or around 800kg at 8g/cm^2. Now,
> that's a conservative number because aluminum is not actually the best
> shielding; something with a lot of hydrogen in it will be better.
Water has a lot of hydrogen but unlike polyethylene it can be moved
around easily. If you store a layer of water in the walls and then use
it for evaporative cooling during reentry you can theoretically use the
same mass for both radiation shielding and heat shielding. Is there a
potential net mass gain here?
The lunar lander also needs significant radiation shielding and all
that mass is carried down into the moon's gravity well and up again
anyway. If it doubles as your reentry heat shield the mass penalty of a
direct return architecture is potentially reduced.
Evaporative cooling is usually mentioned as a heavier but reusable TPS
alternative. Could it make sense in a lunar mission capsule for
different reasons?
Oren
Henry Spencer
Oren <or...@hishome.net> wrote:
>> that's a conservative number because aluminum is not actually the best
>> shielding; something with a lot of hydrogen in it will be better.
>
>Water has a lot of hydrogen but unlike polyethylene it can be moved
>around easily. If you store a layer of water in the walls and then use
>it for evaporative cooling during reentry you can theoretically use the
>same mass for both radiation shielding and heat shielding. Is there a
>potential net mass gain here?
It's mildly interesting even for those modest shielding masses, and much
more so if the shielding requirement is raised to handle giant flares
(which Apollo just took its chances with).
However, water cooling for reentry is poorly explored and a cautious
capsule designer might think it overly risky. (Another area where NASA
could do spaceflight a lot of good with an X-rocket series, sigh.)
>The lunar lander also needs significant radiation shielding and all
>that mass is carried down into the moon's gravity well and up again...
Whether the lander needs significant shielding is not clear. Apollo did
*not* shield its lander; the procedure for a major flare was for the guys
on the surface to head back to the CSM pronto, as soon as the radiation
gauges started to rise. If you can do that at any time, and you think
you'll have enough time for it(*), you may not want to shield the lander.
(* The joker in the deck is the 20 Jan 2005 flare, which was the most
intense in spaceflight history *and* hit like an avalanche, with none of
the long slow rise seen in other giant flares. That caused a lot of
rethinking of radiation-protection ideas. )
An alternative is to adopt the philosophy that the lander is only for
travel, and that the first thing you do on arrival on the lunar surface is
to unload the living quarters and bury them well enough to shield them.
Joe Strout
he...@spsystems.net (Henry Spencer) wrote:
> An alternative is to adopt the philosophy that the lander is only for
> travel, and that the first thing you do on arrival on the lunar surface is
> to unload the living quarters and bury them well enough to shield them.
Or perhaps even better, land your living quarters and bury them with
remotely-operated bulldozers well before your crews arrive. I'm not one
to claim that robots (remotely operated or not) can do anything people
can do... but heaping regolith up over a hab seems pretty doable.
Best,
- Joe
Mike Combs
news:joe-DC6A5C.1...@comcast.dca.giganews.com...
>
> Or perhaps even better, land your living quarters and bury them with
> remotely-operated bulldozers well before your crews arrive. I'm not one
> to claim that robots (remotely operated or not) can do anything people
> can do... but heaping regolith up over a hab seems pretty doable.
SSI did some research on remotely operating vehicles with that 1.2 second
signal-delay. They concluded that working with the signal delay was a
learnable skill.
--
Regards,
Mike Combs
----------------------------------------------------------------------
By all that you hold dear on this good Earth
I bid you stand, Men of the West!
Aragorn
Joe Strout
"Mike Combs" <mike...@nospam.com_chg_nospam_2_ti> wrote:
> "Joe Strout" <j...@strout.net> wrote in message
> news:joe-DC6A5C.1...@comcast.dca.giganews.com...
> >
> > Or perhaps even better, land your living quarters and bury them with
> > remotely-operated bulldozers well before your crews arrive. I'm not one
> > to claim that robots (remotely operated or not) can do anything people
> > can do... but heaping regolith up over a hab seems pretty doable.
>
> SSI did some research on remotely operating vehicles with that 1.2 second
> signal-delay. They concluded that working with the signal delay was a
> learnable skill.
Right (especially if you don't need to be in a hurry to get the job
done). If there were any doubt about this, one could easily make a
computer game that simulates it. Give this to a teenager, and come back
the next day to see a master operator. :)
Best,
- Joe
Greg D. Moore (Strider)
Reminds me of a short sci-fi story where teenage game players were used to
fight a nuclear war.
>
> Best,
> - Joe
Henry Spencer
Joe Strout <j...@strout.net> wrote:
>> ...the first thing you do on arrival on the lunar surface is
>> to unload the living quarters and bury them well enough to shield them.
>
>Or perhaps even better, land your living quarters and bury them with
>remotely-operated bulldozers well before your crews arrive. I'm not one
>to claim that robots (remotely operated or not) can do anything people
>can do... but heaping regolith up over a hab seems pretty doable.
Yes, that's the sort of simple job that teleoperation is reasonably up
to handling. The one real worry would be whether the robodozers can run
long enough without maintenance.
Henry Spencer
>signal-delay. They concluded that working with the signal delay was a
>learnable skill.
2.5 seconds for the round trip. And the earlier and more definitive
research on the matter was done by the Lunokhod operating crews... :-)
(Mind you, only recently has some of that experience filtered out to the
rest of the world.) They found it stressful but practical.
Alex Terrell
Henry Spencer wrote:
> In article <joe-DC6A5C.1...@comcast.dca.giganews.com>,
> Joe Strout <j...@strout.net> wrote:
> >> ...the first thing you do on arrival on the lunar surface is
> >> to unload the living quarters and bury them well enough to shield them.
> >
> >Or perhaps even better, land your living quarters and bury them with
> >remotely-operated bulldozers well before your crews arrive. I'm not one
> >to claim that robots (remotely operated or not) can do anything people
> >can do... but heaping regolith up over a hab seems pretty doable.
>
> Yes, that's the sort of simple job that teleoperation is reasonably up
> to handling. The one real worry would be whether the robodozers can run
> long enough without maintenance.
> --
All the images are of geologists out exploring, but most of the crew
will top notch mechanics working in pressurisable garages to fix all
the teleoperated and autonomous stuff that has gone wrong.
Today's astronauts are wrongly qualified for this type of job.
kert
> In article <joe-DC6A5C.1...@comcast.dca.giganews.com>,
> Joe Strout <j...@strout.net> wrote:
> >> ...the first thing you do on arrival on the lunar surface is
> >> to unload the living quarters and bury them well enough to shield them.
> >
> >Or perhaps even better, land your living quarters and bury them with
> >remotely-operated bulldozers well before your crews arrive. I'm not one
> >to claim that robots (remotely operated or not) can do anything people
> >can do... but heaping regolith up over a hab seems pretty doable.
>
> Yes, that's the sort of simple job that teleoperation is reasonably up
> to handling. The one real worry would be whether the robodozers can run
> long enough without maintenance.
Suprising amount of work in modern surface mining is automated, and
equipment manufacturers have achieved incredible reliability figures.
As to space, the prototype machines are just into their first or second
generations but are showing some promise:
http://www.isruinfo.com/index.php?page=srr_8
-kert
Henry Spencer
kert <kaid...@gmail.com> wrote:
>> Yes, that's the sort of simple job that teleoperation is reasonably up
>> to handling. The one real worry would be whether the robodozers can run
>> long enough without maintenance.
>
>Suprising amount of work in modern surface mining is automated, and
>equipment manufacturers have achieved incredible reliability figures.
The lunar surface is considerably more hostile than Earth-surface mining,
notably because the dust gets everywhere and is highly abrasive. A year
or so ago I had the chance to ask Steve Gillett -- a professional mining
geologist with an interest in space -- about this, and he said that while
there is some Earthly experience in highly-abrasive environments, it's not
encouraging: operations there tend to be very maintenance-intensive.
The mining engineers and the vehicle engineers almost unanimously think
that the aerospace engineers are laughably optimistic about their ability
to solve such problems without lengthy experimentation on the lunar
surface. (The chemical engineers have similar opinions about aerospace
engineers' attempts to design lunar chemical plants.) The first two or
three generations of surface equipment are likely to be very unreliable
and need a lot of maintenance.
Derek Lyons
>The mining engineers and the vehicle engineers almost unanimously think
>that the aerospace engineers are laughably optimistic about their ability
>to solve such problems without lengthy experimentation on the lunar
>surface.
Why shouldn't aerospace engineers be laughably optimistic about things
outside their area of 'competence'? They're equally so _within_ said
area.