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#20
by
Proponent
on 18 Dec, 2013 23:05
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What makes Orion so heavy, anyway? AIUI, the Orion CM is intended to tip the scales at 22 klb (I presume--see the attached doc--that's
after the weight is reduced to get it down to what its 'chutes can support). The Apollo CM, in comparison, was a waif at 13 klb. You'd expect Orion might be heavier because it has a crew of four rather than Apollo's three, but on the other hand technology, particularly electronics, has moved on quite a bit since the 1960s. Orion might also support its crew for a bit longer than Apollo, but that's probably mostly a matter of weight in the SM, not the CM. I don't get it.
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#21
by
Lars_J
on 19 Dec, 2013 00:32
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What makes Orion so heavy, anyway? AIUI, the Orion CM is intended to tip the scales at 22 klb (I presume--see the attached doc--that's after the weight is reduced to get it down to what its 'chutes can support). The Apollo CM, in comparison, was a waif at 13 klb. You'd expect Orion might be heavier because it has a crew of four rather than Apollo's three, but on the other hand technology, particularly electronics, has moved on quite a bit since the 1960s. Orion might also support its crew for a bit longer than Apollo, but that's probably mostly a matter of weight in the SM, not the CM. I don't get it.
Some of it is basic physics... Orion is a scaled up Apollo. From 3.9m diameter to 5m diameter. A 28% increase in diameter.
But that is a ~120% increase in volume. So in overly simple terms, if Orion was made from Apollo materials it should weigh ~27 klb. So Orion isn't doing *that* bad. But still, one would expect it do do even *better*.
Part of the problem may be that the Apollo shape simply doesn't scale up very well.
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#22
by
TomH
on 19 Dec, 2013 05:20
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What makes Orion so heavy, anyway? AIUI, the Orion CM is intended to tip the scales at 22 klb (I presume--see the attached doc--that's after the weight is reduced to get it down to what its 'chutes can support). The Apollo CM, in comparison, was a waif at 13 klb. You'd expect Orion might be heavier because it has a crew of four rather than Apollo's three, but on the other hand technology, particularly electronics, has moved on quite a bit since the 1960s. Orion might also support its crew for a bit longer than Apollo, but that's probably mostly a matter of weight in the SM, not the CM. I don't get it.
Some of it is basic physics... Orion is a scaled up Apollo. From 3.9m diameter to 5m diameter. A 28% increase in diameter.
But that is a ~120% increase in volume. So in overly simple terms, if Orion was made from Apollo materials it should weigh ~27 klb. So Orion isn't doing *that* bad. But still, one would expect it do do even *better*.
Part of the problem may be that the Apollo shape simply doesn't scale up very well.
You both raise great points. And remember, Orion is capable of accommodating 6 astronauts in a differing configuration. Rather than going from 5.0 up to the 5.5 m diameter, it would have been better to reduce the diameter for accommodating only 4 astros. Everything that can possibly go into a SM should be there instead of inside the CM. CST-100 has the same shape, but is 4.56 m diameter, mass is ca. 10 tons and can accommodate 6. It's TPS is designed for about 17,300 mph reentry interface following deorbit burn, while Orion's is rated for 32,000 mph Mars reentry, so the TPS is some of the mass difference. Still, the comparison with CST-100 is more revealing than with Apollo. This is why Orion seems IMHO anyway to be over massed and also why it seems reasonable that NASA at least consider looking at the trades involved in leaving Orion behind on a Mars mission, opting to use a taxi and to send a tanker to rendezvous with the hab as it approaches Earth on return prior to EOI in cis-Lunar space. Otherwise, think about an Aldrin cycler; let the higher mass vehicle maintain its inertia and send a high V crew transfer vehicle to rendezvous with it.
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#23
by
Proponent
on 19 Dec, 2013 08:04
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What makes Orion so heavy, anyway? AIUI, the Orion CM is intended to tip the scales at 22 klb (I presume--see the attached doc--that's after the weight is reduced to get it down to what its 'chutes can support). The Apollo CM, in comparison, was a waif at 13 klb. You'd expect Orion might be heavier because it has a crew of four rather than Apollo's three, but on the other hand technology, particularly electronics, has moved on quite a bit since the 1960s. Orion might also support its crew for a bit longer than Apollo, but that's probably mostly a matter of weight in the SM, not the CM. I don't get it.
Some of it is basic physics... Orion is a scaled up Apollo. From 3.9m diameter to 5m diameter. A 28% increase in diameter.
But that is a ~120% increase in volume. So in overly simple terms, if Orion was made from Apollo materials it should weigh ~27 klb. So Orion isn't doing *that* bad. But still, one would expect it do do even *better*.
Part of the problem may be that the Apollo shape simply doesn't scale up very well.
But that begs the question of why is it so much larger than Apollo? Is there a good reason for requiring so much more volume per crew member than Apollo offered? Particularly since for any extended mission, additional modules are required anyway. For that matter, come to think of it, is there a firm justification for increasing the crew to four from Apollo's three? Obviously there are advantages to a larger crew -- when you get to the moon or Mars you get more person-hours per mission on the surface -- but did anybody ever rigorously trade those advantages against the costs?
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#24
by
darkbluenine
on 19 Dec, 2013 13:32
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For that matter, come to think of it, is there a firm justification for increasing the crew to four from Apollo's three?
Safety during lunar surface operations. The logic is that astronauts should work in teams of two in the event one experiences an accident or equipment failure. They should always have a partner to back them up. (The two teams also back each other up in the event there's an accident or equipment failure that strands one team.)
With no astronaut staying on the CM as was done during Apollo, that third astronaut will be on the surface and needs a partner (a fourth astronaut) to engage in surface operations safely.
Obviously there are advantages to a larger crew -- when you get to the moon or Mars you get more person-hours per mission on the surface
Mars missions usually assume six astronauts due to the long duration of the mission and the skill mix needed. The logic is that it's probably unrealistic for four astronauts to possess all the necessary skills for a mission of that duration and complexity.
-- but did anybody ever rigorously trade those advantages against the costs?
No. It was an assumption in ESAS. From page 18 in the report:
1.2.3 Technical GR&As
The Technical GR&As are listed below.
• The CEV will be designed for up to a crew of six for ISS missions.
• The CEV will be designed for up to a crew of four for lunar missions.
• The CEV will be designed for up to a crew of six for Mars missions.
The total lack of analysis of the sensitivity of cost and safety to requirements, including crew size, was a major weakness of the ESAS effort. More astronauts and safer surface operations are great until they push you out of the budget box and beyond parachute limits and technology.
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#25
by
Proponent
on 19 Dec, 2013 14:47
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OK, thanks, it makes a little more sense now. I had erroneously believed that the requirement to carry a crew of six applied only for ISS taxi missions. In that case, since the basic Apollo CM was capable of returning five to earth in a pinch and since there was a North American proposal in 1966 squeeze six astros in for LEO taxi missions (with touch-down on dry land, no less -- see David Shayler's book Apollo: Lost and Forgotten Missions), I couldn't see why Orion would require so much more volume. But if the requirement is to carry six on longer voyages (though surely not all the way to Mars without a hab module!), the much greater volume makes more sense.
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#26
by
pathfinder_01
on 19 Dec, 2013 22:03
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I couldn't see why Orion would require so much more volume. But if the requirement is to carry six on longer voyages (though surely not all the way to Mars without a hab module!), the much greater volume makes more sense.
The reason for the increased volume is to support 4 people for 21 days. Apollo only had to support 3 people for 14 days. Orion needs to support a crew 7 days longer and with one extra person than Apollo. This increases the amount of supplies needed. In fact the volume of the capsule is too small for current life support systems (ones that use lioh) and too small for ISS style regenerative systems and so they had to develop smaller life support systems for it(something they were not planning to do.).
Basically taking the same shape, scaling it up and stuffing an extra person in and expecting it to keep a crew longer may have been too much to do. They didn’t want to put the extra supplies in another module(like Soyuz) because they thought having everything in one module would be safer than separating from an orbital module or docking/undocking. Basically this decision is biting them in the rear at the moment(too heavy for the chutes, and too small for life support tech. to bear this load, causing unexpected spending.)
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#27
by
Raj2014
on 24 Jul, 2014 20:46
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What is the length of the Orion and apollo spacecrafts?
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#28
by
MATTBLAK
on 24 Jul, 2014 21:03
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With it's huge engine bell and long, propellant laden service module, Apollo would be a bit longer than the Orion CM & SM combo I should think. Incidentally, I've always thought the Orion CM is too large - it should have been no wider than 4.5 meters (like CST-100) or better yet, just 4 meters like Apollo. And if NASA and it's contractor had been brave enough; a composite main structure to save weight. A 4 meter, composite Orion should have no issues with high mass at all and be able to be launched on a variety of boosters. It would not matter if Orion was smaller than 5 meters; as it should always be/have only been a launch, control cockpit and re-entry vehicle (Soyuz?), not a jack-of-all trades that it seems to be portrayed as right now.
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#29
by
Steven Pietrobon
on 25 Jul, 2014 07:54
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The Apollo CSM length is 11.03 m. I couldn't find a source for the Orion length, but using an Orion heat shield diameter of 5.03 m and the attached image, I get a length of about 7.84 m. Thus, Orion is about 3.19 m or 29% shorter than the Apollo CSM.
I agree about Orion being too wide. However, I believe that a Soyuz type system would have provided a lower total mass with substantially increased internal volume. This is especially useful for Lunar missions. For Mars or asteroid missions, the orbital module is replaced with a larger habitat, again saving mass. A nominal design with a 3.3 m diameter is given below. Attached is the program I used. I get an 8.76 t or 38% reduction in total mass while total internal volume increases by 108%.
Soyuz Shenzhou Orion Orion2
mass capsule (t) 2.95 3.24 9.82 3.90
mass orbital module (t) 1.30 1.50 - 1.97
mass service module (t) 2.10 2.10 3.80 2.52
mass space craft (t) 6.35 6.84 13.62 8.39
mass propellant (t) 0.80 1.00 9.20 5.67
mass total (t) 7.15 7.84 22.82 14.06
volume capsule (m^3} 3.5 6.0 9.0 8.2
volume orbital module (m^3) 5.0 8.0 - 10.5
volume total (m^3) 8.5 14.0 9.0 18.7
diameter (m) 2.17 2.52 5.03 3.31
Crew 3 3 4 4
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#30
by
TomH
on 27 Jul, 2014 04:11
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... I believe that a Soyuz type system would have provided a lower total mass with substantially increased internal volume. This is especially useful for Lunar missions. For Mars or asteroid missions, the orbital module is replaced with a larger habitat, again saving mass....
Completely agreed. Orion was designed to serve as both reentry capsule and habitat for lunar missions. Soyuz design has minimal mass and volume in the reentry capsule, just big enough for 3 persons to survive reentry and just enough consumables for the short duration of reentry. The extra volume in the hab section is used at other times. Orion designers had in mind one vehicle that would serve both purposes. It can still serve both purposes on a lunar mission, but it is not well designed for a Mars mission because another hab is required anyway. Steven is right. The reentry capsule should be just big enough for that purpose. A small hab should go along on lunar missions and a big hab on Deep space missions.
To answer the questions about what makes Orion over mass: parachutes. Orion is too heavy for its parachutes. It is pushing the boundaries for parachutes to safely function. I don't remember all the technical details, but ISTR that making the chutes bigger doesn't solve the problem. Apparently there is a limit to how much weight 3 chutes can safely bring down and adding or enlarging chutes doesn't help the problem. The original big Orion would have been eventually cancelled no matter what because it had far too much mass for the chutes to handle.
Going to a Soyuz type design would lower mission mass as well as solve the parachute problem.
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#31
by
M_Puckett
on 27 Jul, 2014 04:29
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Why not add a fourth chute?
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#32
by
TomH
on 27 Jul, 2014 04:45
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Why not add a fourth chute?
I wondered the same thing. I don't know for certain, but it may have to do with the likelihood that the chutes would tangle with each other or the angular number of degrees the chutes divert from the vertical axis. Hopefully someone with more knowledge will chip in.
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#33
by
RonM
on 27 Jul, 2014 04:53
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Why not add a fourth chute?
I wondered the same thing. I don't know for certain, but it may have to do with the likelihood that the chutes would tangle with each other or the angular number of degrees the chutes divert from the vertical axis. Hopefully someone with more knowledge will chip in.
Not only that, but where would you put a fourth chute? It's already a tight fit for three chutes.
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#34
by
Burninate
on 27 Jul, 2014 05:33
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What is the actual issue with scaling up chutes to higher loading? What is the failure mode associated with the present chutes being too small, or with doubling the size of the existing chutes?
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#35
by
Lars_J
on 27 Jul, 2014 05:47
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Why not add a fourth chute?
I wondered the same thing. I don't know for certain, but it may have to do with the likelihood that the chutes would tangle with each other or the angular number of degrees the chutes divert from the vertical axis. Hopefully someone with more knowledge will chip in.
Not only that, but where would you put a fourth chute? It's already a tight fit for three chutes.
Indeed... It might require them to build something a bit more different than Apollo. If only we didn't have to build new capsules just like Apollo.
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#36
by
TomH
on 27 Jul, 2014 05:56
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What is the actual issue with scaling up chutes to higher loading? What is the failure mode associated with the present chutes being too small, or with doubling the size of the existing chutes?
Indeed, although apparently problems with doing those things do exist. Sounds like this might make an interesting article for Chris or one of his proteges to address. Any possibility of a short article that could explain why these solutions won't work for the mass/parachute problem, Chris?
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#37
by
Raj2014
on 27 Jul, 2014 09:51
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Are there any pictures of what the Original Orion capsule would have looked liked?
I found these websites,
website 1,
website 2,
website 3 and
website 4. Is this the original spacecraft?
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#38
by
A_M_Swallow
on 27 Jul, 2014 16:50
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Indeed... It might require them to build something a bit more different than Apollo. If only we didn't have to build new capsules just like Apollo.
Unless we make it exactly the same shape and size as the Apollo Command Module.
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#39
by
Rocket Science
on 27 Jul, 2014 22:10
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Perhaps they could revisit the original parafoil proposal vs the chutes...
