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#20
by
notsorandom
on 19 Jul, 2016 19:41
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There is no need to bring any Orions along for the ride. A simple mission like this could be staged out of L1, L2, or DRO. Have the crew launch on Orion out there to meet the Mars bound spacecraft. The return the crew to one of these places to meet up with a waiting return craft. The interplanetary craft would consist of the DSP, SEP tug, and possibly a hypergolic chemical propulsion system. The same SEP tug could raise the interplanetary craft out of LEO where it could be assembled using smaller launch vehicles.
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#21
by
KelvinZero
on 20 Jul, 2016 06:30
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There is no need to bring any Orions along for the ride. A simple mission like this could be staged out of L1, L2, or DRO. Have the crew launch on Orion out there to meet the Mars bound spacecraft. The return the crew to one of these places to meet up with a waiting return craft.
Doesn't that imply either that the Orion can survive in space for the duration of the mission anyway, or an additional launch of an Orion, probably on an SLS? Also an extra rendezvous in either case.
How much mass would the Orion add, proportionally? I had assumed the DSH was fairly big, so the Orion would only add a bit of inefficiency. You add 25% more volume say, and that 25% is 1/3 heavier than if it had been designed purely for in-space.. something like that. Those numbers are pulled out of a hat..anyone got better ones?
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#22
by
MATTBLAK
on 20 Jul, 2016 08:23
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Orion could only go along, all the way to Mars, if it had a heatshield and other, multiple systems upgrades. If there were a Gateway Station at L-2, then the Orion would only need to go that far - taking crews to and from the DSH and other Mars-bound components. The other, famous capsule craft we all know about (
) is supposed to be able to withstand a good, long 2-year 'space soak' and is also supposed to have a heatshield good enough to withstand a direct Earth entry, coming back from deep space.
If the Orion was to act as a Mars Mission 'Command & Control Module'
and Earth Return Vehicle, then it's likely it's Service Module would need upgrades and increased propellant loads and both the CM & SM would need redesign so their hypergolic propulsion systems wouldn't degrade from more than 12 months in deep space. Such upgrades to Orion wouldn't come cheap - and would that be a 'Block III' or IV version of the craft? And would it need to perform a fair sized 'slow down' burn to make it safely down to Earth?
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#23
by
RonM
on 20 Jul, 2016 14:12
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Since NASA isn't planning on going to Mars until the 2030s, there is plenty of time for Orion upgrades if needed.
I prefer the idea of a gateway station, but it might not fit NASA's budget. Earlier Mars mission plans did have Orion as the "command and control module."
Satellites and probes use hypergolic systems for very long mission durations. They don't degrade in 12 months.
No need for a slow down burn with a proper heatshield.
If "the other famous capsule" can be built to solve these issues, then why can't Orion be upgraded?
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#24
by
the_other_Doug
on 20 Jul, 2016 14:54
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Guys? A lot of us non-engineers are playing Kerbal with this -- we're taking one or two statements from various sources, out of context, and pretending that they are in the little postage-stamp listing of capabilities and limitations of the building blocks we're looking at with Orion and NASA's Mars architecture.
The discussion is also just playing with one or two elements -- a heat shield that has not been rated or tested at the high end of direct entry from a Mars transfer orbit, for example, and an Orion SM that can't support the spacecraft for more than a month or two, and as such, the remaining systems aren't tweaked to be able to shut down for long stretches and then brought back online. And that's because these systems were never designed to operate for years at a time without being attached to a larger architecture.
The basic Orion design does not in any way preclude the relatively minor tweaks needed to support bringing an Orion along all the way to LMO and back. This does not require a thorough redesign of the spacecraft systems. If, indeed (for example), the current Orion heat shield material won't survive projected worst-case direct entry speeds, then we have, what, another 10 years to develop, test and implement a heat shield that can do so. It won't be needed for at least a decade, per NASA's funding-starved schedules. Even the proposed Orion+DSH mission being discussed here wouldn't launch for another eight years -- still plenty of time to develop the heat shield and other tweaks needed, if one chose to fly this mission.
So, it's just as disingenuous to state, as of 2016, that Orion is not capable of coming back from Mars (and making the logical error of extending that to say that, therefore, Orion will never be capable of it) as it is to say that Dragon is not currently capable of propulsive landings, and therefore will never be capable of them. See my point?
And to counter the argument "Well, SpaceX is planning for propulsive entries, but NASA doesn't have any plans to beef up Orion's heat shield," I will just say that NASA currently plans to bring Orion to LMO and back, and the DRM currently includes a direct entry of the Orion from the trans-Earth trajectory. Using just a little logic (a skill some of us could use to learn), we see that NASA cannot be planning what they are planning unless they are also planning on applying all mods to Orion (including to the heat shield) that are needful to accomplish the mission.
Also, NASA, at least, is always all about contingencies and abort modes, when it comes to placing humans in space. I can think of a number of different trans-Earth coast abort modes that would make it nearly impossible to maneuver to a rendezvous with the only thing capable of surviving entry into Earth's atmosphere in cislunar space, but does leave you the ability to aim with some precision at a direct entry corridor. (And no -- don't even start with "Then we just send a <insert non-Orion entry capsule name here> to rendezvous with the incoming spacecraft." Just try modeling that kind of trajectory -- you'd either need to launch such a rescue vehicle years before you launch the Orion to Mars, just in case, or you'd need several BFSes all connected together to get something into the same inbound trajectory without starting out at Mars in the first place.)
I wouldn't want to be heading back to Earth from Mars, in a spacecraft that cannot enter an atmosphere, when my main propulsion goes out and I am reduced to the choices of shooting off into solar orbit, or at least having my constituents return to Earth in a blazing fireball.
For safety reasons and for contingency planning to reduce the likelihood of loss of crew, any spacecraft they bring back from Mars with people in it will have the ability to bring those people directly back through the atmosphere, to a safe landing on Earth. If that's not the Orion, then they will feel forced to develop, at much greater expense, a lifeboat or escape pod configuration that gives the crew a way to come back without needing to rendezvous with a return vehicle.
Now, balance the expense and complication of developing such a lifeboat against simply upgrading Orion's heat shield (and tweaking the SM's systems to support quiescent hibernation for periods of up to three years) and taking it to Mars and back.
I'll bet you anything that applying the needed tweaks to Orion come out to be far more economical than any other approach. And, bottom line, I just cannot see NASA bringing people back from Mars in a ship that cannot guarantee their safe return without any additional self-powered rendezvous maneuvers. It would add a lot of potential single-point failures that could result in complete LOCV. And that's the one thing I can't see NASA ever doing...
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#25
by
Robotbeat
on 20 Jul, 2016 18:26
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Hey, engineers of the past would've KILLED for a simulator like Kerbal.
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#26
by
A_M_Swallow
on 20 Jul, 2016 19:19
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Hey, engineers of the past would've KILLED for a simulator like Kerbal.
Kerbal may not be perfect but it allows engineers to experiment cheaply and gets rid of the the silly options. Its outfeeds allow more detailed simulators to start with a good second approximation.
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#27
by
AncientU
on 20 Jul, 2016 21:41
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The back end of the Asteroid Redirect Robotic Mission (ARRM) spacecraft is a Solar Electric Propulsion (SEP) tug. This is due to be launched in December 2021. So by about 2021 NASA will be able to buy SEP tugs.
The tug design may need upgrading to reach human rating standards.
NASA can buy SEP tugs now if it wants to. See Dawn.
Is a 0.09Newton (0.02lbf) 'SEP tug' for a 212 tonne (466,400lb) mission a bit undersized for a manned mission in deep space rad environment?
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#28
by
Robotbeat
on 21 Jul, 2016 01:53
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The back end of the Asteroid Redirect Robotic Mission (ARRM) spacecraft is a Solar Electric Propulsion (SEP) tug. This is due to be launched in December 2021. So by about 2021 NASA will be able to buy SEP tugs.
The tug design may need upgrading to reach human rating standards.
NASA can buy SEP tugs now if it wants to. See Dawn.
Is a 0.09Newton (0.02lbf) 'SEP tug' for a 212 tonne (466,400lb) mission a bit undersized for a manned mission in deep space rad environment?
The NSTAR thruster is fairly low-power at 2.3kW. But commercial units are at least 4.5kW and can be ganged together. And the NEXT thruster is 7kW. Gang 15 together, and you have >100kW, which is good enough for a basic tug.
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#29
by
Mark S
on 21 Jul, 2016 15:35
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The back end of the Asteroid Redirect Robotic Mission (ARRM) spacecraft is a Solar Electric Propulsion (SEP) tug. This is due to be launched in December 2021. So by about 2021 NASA will be able to buy SEP tugs.
The tug design may need upgrading to reach human rating standards.
NASA can buy SEP tugs now if it wants to. See Dawn.
Is a 0.09Newton (0.02lbf) 'SEP tug' for a 212 tonne (466,400lb) mission a bit undersized for a manned mission in deep space rad environment?
The NSTAR thruster is fairly low-power at 2.3kW. But commercial units are at least 4.5kW and can be ganged together. And the NEXT thruster is 7kW. Gang 15 together, and you have >100kW, which is good enough for a basic tug.
I'm not sure why you're quoting power consumption when AncientU's question was about thrust. I suppose a ~46x increase in power consumption would translate to a similar increase in thrust. Assuming an increase in efficiency (NEXT over NSTAR) between 0% and 100%, that would still only come out to somewhere between 0.9 and 1.8 lbf of total thrust. Would that be suitable for a 212 tonne mission stack? What would the Mars transit time be, assuming constant thrust?
Thanks.
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#30
by
Robotbeat
on 21 Jul, 2016 17:30
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Power and thrust are proportional to each other, and the proportionality constant is exhaust velocity. THAT'S why I said power.
Power = thrust*exhaustvelocity
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#31
by
Mark S
on 21 Jul, 2016 19:46
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Power and thrust are proportional to each other, and the proportionality constant is exhaust velocity. THAT'S why I said power.
Power = thrust*exhaustvelocity
Thanks, that (proportionality) is pretty much what I figured, as you can see from my post. However, now I'm curious as to the power ratings of the thrusters that you mentioned. Is that the power output of the thruster, using the equation you gave? Or is it the electrical power input required to operate the thruster at the given thrust level? When you stated the thrusters' power levels in watts, I thought it was the latter. Given the context of your reply, it would seem to be the former.
Anyway, the bottom line seems to be that you need ~1 MW of power for every 10 lbf of thrust. Please correct me if my math is wrong, or if I have a bad understanding of the underlying principles.
Thanks again.
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#32
by
A_M_Swallow
on 21 Jul, 2016 21:25
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Ion Thruster Information
NSTARPropellant Xenon
Power 2.3 kW
Isp 3,300 to 1,700 s
Max Thrust 92 mN
NEXTPropellant Xenon
Power 6.9 kW
Isp 4,190 s
Max Thrust 236 mN
Ref:
https://en.wikipedia.org/wiki/Ion_thrusterOn interplanetary trips solar power is not constant. This affects both the design of the spacecraft and route planning. Power from the solar panels drops to (nearly) zero when in the shadow of the Earth or Mars. The time in shadow per orbit varies with height. The power received from the sun falls off according to an inverse square law.
Solar power at Earth orbit 1,413 Wm
-2Solar power at Mars orbit 715 Wm
-2Ref:
https://en.wikipedia.org/wiki/Sunlight
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#33
by
Robotbeat
on 22 Jul, 2016 19:30
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Power and thrust are proportional to each other, and the proportionality constant is exhaust velocity. THAT'S why I said power.
Power = thrust*exhaustvelocity
Thanks, that (proportionality) is pretty much what I figured, as you can see from my post. However, now I'm curious as to the power ratings of the thrusters that you mentioned. Is that the power output of the thruster, using the equation you gave? Or is it the electrical power input required to operate the thruster at the given thrust level? When you stated the thrusters' power levels in watts, I thought it was the latter. Given the context of your reply, it would seem to be the former.
Anyway, the bottom line seems to be that you need ~1 MW of power for every 10 lbf of thrust. Please correct me if my math is wrong, or if I have a bad understanding of the underlying principles.
Thanks again.
Keep in mind that thrust goes up if you reduce Isp. It's super basic physics. You can build an electric thruster that gets 30 pounds of thrust with 1MW if you reduce the Isp. Or really, just use base SI, and you don't have to use any of these "rules of thumb" or "bottom lines." And heck, just use exhaust velocity. I think Isp (in s) will eventually be deprecated.
1MW/(10km/s) = 1,000,000 Watts/(10,000 m/s) = 100 Newtons. Super simple.
Or if you operate at very high exhaust velocity, like 100km/s (10,000s Isp), it's:
10^6 W/(10^5 m/s) = 10 N.
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#34
by
corneliussulla
on 15 Apr, 2017 11:54
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Falcon Heavy can put 64 tonnes in LEO. For 100 mill. Surely NASA should drop the SLS and just work out a way to send the DSH , Orion etc up on top the falcon heavy, just think of the extra exploration missions they could run with the money they saved. SLS is dead in the water, 40 year old technology with a huge price tag.
Many of the NASA exploration parts could be put into space with falcon heavy recovery of the first stages. That should make it cheaper again.
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#35
by
Archibald
on 15 Apr, 2017 20:15
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What most people fell to appreciate is that the Falcon 9 Heavy, with its kerolox upper stage, has low performance beyond LEO. nothing beats LH2 there.
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#36
by
envy887
on 16 Apr, 2017 16:00
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What most people fell to appreciate is that the Falcon 9 Heavy, with its kerolox upper stage, has low performance beyond LEO. nothing beats LH2 there.
NASA seems to plan on staging in cislunar space, which is rather easily accessible to kerolox and hypergol stages. FH has very similar performance to TLI as SLS Block 1 and, most likely, 3-stage New Glenn. SLS Block 1B will be ~50% higher.
Performance direct to TMI doesn't seem to be critical to any planned architecture.
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#37
by
Robotbeat
on 17 Apr, 2017 19:40
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What most people fell to appreciate is that the Falcon 9 Heavy, with its kerolox upper stage, has low performance beyond LEO. nothing beats LH2 there.
So what? Stage in LEO. We have lots more experience there anyway.
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#38
by
Patchouli
on 20 Apr, 2017 03:59
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What most people fell to appreciate is that the Falcon 9 Heavy, with its kerolox upper stage, has low performance beyond LEO. nothing beats LH2 there.
True.
OT but I'm surprised Spacex never designed a third stage for the Falcon vehicles as even something like a Star derivative would help enormously on high energy orbits.
So what? Stage in LEO. We have lots more experience there anyway.
Assembly in LEO would make it easier for commercial involvement.
Things like automated docking and telerobotics is a lot easier in LEO as well.
Chemical and nuclear thermal departure stages can make use of the Oberth effect in LEO.
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#39
by
envy887
on 25 Apr, 2017 15:51
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What most people fell to appreciate is that the Falcon 9 Heavy, with its kerolox upper stage, has low performance beyond LEO. nothing beats LH2 there.
True.
OT but I'm surprised Spacex never designed a third stage for the Falcon vehicles as even something like a Star derivative would help enormously on high energy orbits.
It really wouldn't help enormously, though. A STAR-48 would increase payload to GTO by ~25%. The v1.0 to Block 5 upgrades have increased it over 300%. FH will offer more payload to GTO, TLI, or TMI than any existing rocket including those with LH2 stages. It's not enough to do a hab+capsule flyby mission in one launch, but a dual-launch could work.
) is supposed to be able to withstand a good, long 2-year 'space soak' and is also supposed to have a heatshield good enough to withstand a direct Earth entry, coming back from deep space.