Author Topic: NASA examines options and flight paths for SLS EM-2 mission  (Read 31178 times)

Offline Chris Bergin

https://www.nasaspaceflight.com/2016/03/nasa-examines-options-flight-paths-sls-em-2/

Awesome article by Chris Gebhardt, with additionally cool images from Okan (Nathan) :)

Support NSF via L2 -- Help improve NSF -- Site Rules/Feedback/Updates
**Not a L2 member? Whitelist this forum in your adblocker to support the site and ensure full functionality.**

Offline atomic

  • Member
  • Posts: 17
  • Fort Myers, FL
  • Liked: 10
  • Likes Given: 20
Great article Mr. Gebhardt!
Thank you! A very enjoyable read.

I'm looking forward to a 2022 Europa and 2023 manned SLS moon mission. ;)
« Last Edit: 03/11/2016 05:44 pm by atomic »

Offline Rocket Science

  • Senior Member
  • *****
  • Posts: 10586
  • NASA Educator Astronaut Candidate Applicant 2002
  • Liked: 4548
  • Likes Given: 13523
Thanks for the great update Chris G. and for the eye candy Nathan! 8) With all the "hand-wringing" about putting crew aboard the first flight... :o Easy... keep them at home working the sims, the spacecraft knows what to do... Problem solved...
"The laws of physics are unforgiving"
~Rob: Physics instructor, Aviator

Offline psloss

  • Veteran armchair spectator
  • Senior Member
  • *****
  • Posts: 17980
  • Liked: 4047
  • Likes Given: 2089
Jeff Foust posted this slide from yesterday's NAC meeting (this was from Mr. Gerstenmaier's presentation):
https://twitter.com/jeff_foust/status/804075387416363011

The new wrinkle is the co-manifested payload (CPL) for EM-2 that would need to be available for subsequent exploration missions...so apparently EUS would deploy Orion in a high Earth orbit as noted in this story and then its first "disposal burn" would be a trans-lunar injection burn that would deliver the CPL to a lunar transfer orbit.

(I was traveling yesterday, so didn't hear the discussion that goes along with this slide.  I don't know if this is a new "hybrid" candidate and/or how close this is to being baselined for EM-2.)

Offline sdsds

  • Senior Member
  • *****
  • Posts: 7202
  • “With peace and hope for all mankind.”
  • Seattle
  • Liked: 2050
  • Likes Given: 1962
Excellent to see this article and its description of the hybrid option.

It's a little spooky to see Orion providing its own TLI. Isn't it a bit late in the Orion design effort to be considering this? The requirement would be 443.8 m/s of delta-v I think.
« Last Edit: 12/01/2016 08:10 pm by sdsds »
— 𝐬𝐝𝐒𝐝𝐬 —

Online Steven Pietrobon

  • Member
  • Senior Member
  • *****
  • Posts: 39218
  • Adelaide, Australia
    • Steven Pietrobon's Space Archive
  • Liked: 32738
  • Likes Given: 8192
I don't like this since it puts the crew through the radiation belt many more times than necessary. Also, testing Orion for one day is insufficient for a Lunar mission. Apollo 7 tested the CSM for nearly 11 days in LEO. The CPL will need its own propulsion system to get into Lunar orbit. I'm afraid all the added complexity will cause significant delay to the mission.

My preferred solution is to launch Orion uncrewed to the ISS on a Delta IV Heavy, where crew can transfer to it and perform a 10 day mission in LEO, properly testing all the systems. EM-2 should be a mission that only launches the CPL so that the new Block IB EUS can be tested without risk to the crew. Would be good if the EUS could be made to have low boil-off so that the EUS can perform LOI for the CPL.
« Last Edit: 12/02/2016 04:51 am by Steven Pietrobon »
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline Proponent

  • Senior Member
  • *****
  • Posts: 7277
  • Liked: 2782
  • Likes Given: 1462
It's a little spooky to see Orion providing its own TLI. Isn't it a bit late in the Orion design effort to be considering this? The requirement would be 443.8 m/s of delta-v I think.

Orion's delta-V is about 1500 m/s (or 4920 ft/s, as NASA prefers to put it), so it does seem feasible, with plenty of margin for mid-course corrections.
« Last Edit: 12/02/2016 07:19 am by Proponent »

Offline Proponent

  • Senior Member
  • *****
  • Posts: 7277
  • Liked: 2782
  • Likes Given: 1462

Offline rocx

  • Full Member
  • ***
  • Posts: 383
  • NL
  • Liked: 266
  • Likes Given: 144
At this point, I almost consider EM (the propellantless drive) and EM (the SLS exploration missions) about equally likely.
Any day with a rocket landing is a fantastic day.

Offline Proponent

  • Senior Member
  • *****
  • Posts: 7277
  • Liked: 2782
  • Likes Given: 1462
I don't like this since it puts the crew through the radiation belt many more times than necessary.

Yeah, I wondered about this back when an elliptical check-out orbit was first mooted for EM-2..  After completing one rev in LEO (100 nmi.), the spacecraft will do two revs in a 500 x 19,000-nmi. orbit.  That will entail four passes through both the inner and outer van Allen Belts.  The lunar outbound and trans-Earth legs of the mission will at two more passes, giving a total of six.

But then I had a numerical think about radiation doses during multiple passes through the van Allen Belts once before, in the context of multi-pass aerobraking.  To make a long story short, if you have a look at the last attachment to this post, you'll see that the crew of Apollo 13, which made two passes through both van Allen Belts and, like the proposed EM-2 baseline mission, didn't spent a lot of time near the moon, got skin average doses of 2.4 mGy (1 rad = 0.01 Gy).  Even if you assume that dose came entirely from the van Allen Belts, which, of course, it didn't, then scaling the Apollo 13 results to EM-2's six passes gives a total dose of 7.2 mGy.  That's not a lot:  the Apollo 14 crew, for example, got 11.4 mGy.

Of course, this simple scaling of the Apollo 13 dose is not accurate, for several reasons.  For one, the scatter in the Apollo results is evident.  The dose will depend on solar activity and the inclination of the trajectory with respect to the geomagnetic equator (which wanders with respect to the geographic equator).  And EM-2's elliptical orbits will involve somewhat slower passes through the Belts than do trans-lunar trajectories.  But, especially after you consider that Orion is better shielded than Apollo, I don't think radiation is a big worry.

Why will the perigee be raised from 100 to 500 nmi. for the HEO phase?  Presumably that involves an EUS burn at the first apogee, about seven hours after launch (90 minutes for one rev in LEO plus half of what I make to be a 10.8-hour highly elliptical orbit, the though NASA prose that hektor found seems a little confused on this point).  I'd have thought maintaining a 100-nmi. perigee to be preferable.  Not only is it simpler, but it speeds up the passages through the Belts.

Quote
Also, testing Orion for one day is insufficient for a Lunar mission. Apollo 7 tested the CSM for nearly 11 days in LEO.

The slide mentions that "Free return provides return capability within suit consumables limits (144 hours)"  -- maybe the suits effectively serve as a back-up ECLSS.

Quote
My preferred solution is to launch Orion uncrewed to the ISS on a Delta IV Heavy, where crew can transfer to it and perform a 10 day mission in LEO, properly testing all the systems. EM-2 should be a mission that only launches the CPL so that the new Block IB EUS can be tested without risk to the crew.

That would all seem reasonable.  I think the fundamental problem here is that NASA can afford Orion and SLS only at very low flight rates.  If, as appears to be the case in the near term, Orion and SLS copies are turned out at the rate of just one every two years and the program costs over $3 billion annually, then each additional test in some sense costs $6 billion.  Which is just another way of saying that Orion/SLS does not fit the budget.  Not only is it too expensive to fail, it's even too expensive to test properly -- which increases the probability of failure.
« Last Edit: 12/02/2016 09:18 am by Proponent »

Offline Proponent

  • Senior Member
  • *****
  • Posts: 7277
  • Liked: 2782
  • Likes Given: 1462
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #10 on: 12/02/2016 09:40 am »
It's interesting that the slide mentions "mission extension options post-TLI burn if all systems nominal."  Having already committed ~500 m/s of Orion's 1500 m/s of delta-V, per psloss's calculation, I wonder whether NASA might not want to commit to entering (and leaving) lunar orbit.  Could it be the plan would be just to remain in a highly eccentric orbit for second pass to cis-lunar distance?

Offline Proponent

  • Senior Member
  • *****
  • Posts: 7277
  • Liked: 2782
  • Likes Given: 1462
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #11 on: 12/02/2016 10:12 am »
At this point, I almost consider EM (the propellantless drive) and EM (the SLS exploration missions) about equally likely.

I share you skepticism about the long-term viability of Orion/SLS, but I think its chances for hanging on for at least a few more years have just increased quite a bit, now that pro-commerial spacers Rob Walker and Bob Albrecht are out of Trump team's NASA picture and Chis Shank is in.  Shank's work for Rep. Lamar Smith suggests he is a staunch Orion/SLS man.
« Last Edit: 12/02/2016 10:12 am by Proponent »

Offline DGH

  • Full Member
  • *
  • Posts: 168
  • Liked: 7
  • Likes Given: 4
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #12 on: 12/02/2016 11:30 am »
Can someone explain NASA’s fascination with DRO?
IMO it takes too much time and Delta V to get to from Earth.
IMO it takes too much time and Delta V to get to the Moon from DRO.
L1,L2, NRO  and even High Lunar Orbits looks better IMO.

Offline Proponent

  • Senior Member
  • *****
  • Posts: 7277
  • Liked: 2782
  • Likes Given: 1462
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #13 on: 12/02/2016 12:53 pm »
There's nothing weird about retrograde lunar orbits.  Apollo used them.  At least if you want free-return trajectories, they are easier to reach from Earth than are prograde orbits.  Low lunar orbits require more delta-V to get into or out of than high ones and most are not stable.  High prograde lunar orbits aren't stable either, but high retrograde lunar orbits are.   At the far point (furthest from Earth) of a prograde orbit, the orbital velocity with respect to the moon is is in the same direction as the moon's orbital velocity around the Earth.  Hence, the spacecraft is very weakly bound to the Earth-Moon system and highly subject to perturbing influences like solar gravity.

As to the rationale for choosing lunar DRO over L1 or L2, I'm not sure.
« Last Edit: 12/02/2016 06:18 pm by Proponent »

Online TrevorMonty

Can someone explain NASA’s fascination with DRO?
IMO it takes too much time and Delta V to get to from Earth.
IMO it takes too much time and Delta V to get to the Moon from DRO.
L1,L2, NRO  and even High Lunar Orbits looks better IMO.
There is a Fiso podcast about NRO, looks like it might be preferred orbit. I don't think DRO as location for DSH is set in stone yet.

Over DSH life it may move around based on mission, with SEP it can be relocated to EML1 or EML2 over few months.

Offline sdsds

  • Senior Member
  • *****
  • Posts: 7202
  • “With peace and hope for all mankind.”
  • Seattle
  • Liked: 2050
  • Likes Given: 1962
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #15 on: 12/02/2016 06:40 pm »
DRO was the choice when ARRM might have brought a big asteroid into cis-lunar space. An object in a lunar DRO is not going to "get loose" and smash into the Earth or Moon. Not in literally a million years. Other trajectory regimes don't offer that same level of stability, mainly due to chaotic three-body effects and/or the influence of remote gravitational masses like the Sun.

It seems to me that ARRM also required an insertion trajectory from outside the cis-lunar regime which would "fail safe" in the event of a propulsion failure.
— 𝐬𝐝𝐒𝐝𝐬 —

Offline redliox

  • Senior Member
  • *****
  • Posts: 2539
  • Illinois USA
  • Liked: 683
  • Likes Given: 97
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #16 on: 12/02/2016 11:21 pm »
Chris's article does point out one further item: the Europa Clipper (or whatever it's called) mission is scheduled to target 2022 'officially' now via SLS.  That's a full year before EM-2's flight; on top of that, partly because of the ESM, odds are we can only expect the gap between EM-1 and EM-2 to widen if anything, which presents an opportunity for the Europa mission and an earlier flight of the EUS to be utilized without directly interfering with HSF or the Orion's schedule.

"Let the trails lead where they may, I will follow."
-Tigatron

Offline redliox

  • Senior Member
  • *****
  • Posts: 2539
  • Illinois USA
  • Liked: 683
  • Likes Given: 97
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #17 on: 12/02/2016 11:58 pm »
Although the notion for a mere lunar flyby feels like a cheap cop-out, I can respect one point of it: the loiter in high Earth orbit.  Wasn't there a notion years ago that, during the early flights of Orion, that it was considered wise to check the vehicle out first in an Earth orbit before pushing all the way to the Moon?  It feels like a reflection back to that, which is wise given the uncertainties there are for Orion, especially the ESM and the EUS.  With a live crew on board some caution is merited, although simultaneously with billion-dollar+ flights taxpayers deserve some bang for their buck.

If anything frustrates me aside from delays, I'd say it's the inability to decide what orbit or otherwise where in Cis-Lunar space.  One year it's Lagrange points, another it's Distant Retrograde Orbit, and now this 'Near Rectilinear Orbit' stuff?  Pick a damn orbit for crying out loud!  Better yet, I'd like a better justification for all these differing orbits; everyone seems to say their :insertobscureorbitallosticststermhere: orbit is the most stable and useful nowadays.

I do understand, wherever Orion goes, that it will be limited to some form of high/distant orbit because of the Service Module (European or otherwise).  The high lunar elliptical orbit ranging from 100 km to 10,000 km seems an obvious statement of that.  Obviously, while superior and seemingly more "luxurious" than Apollo, such luxury apparently cost it the ability to directly enter low lunar orbit (although I'd also settle for high lunar orbit with a roomier capsule given same choice).
"Let the trails lead where they may, I will follow."
-Tigatron

Offline sdsds

  • Senior Member
  • *****
  • Posts: 7202
  • “With peace and hope for all mankind.”
  • Seattle
  • Liked: 2050
  • Likes Given: 1962
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #18 on: 12/03/2016 02:40 am »
while superior and seemingly more "luxurious" than Apollo, such luxury apparently cost it the ability to directly enter low lunar orbit

It is probably more accurate to say that in the Constellation architecture the task of lunar orbit insertion was assigned to the Altair lander's propulsion budget rather than the Orion SM propulsion budget. (That was because Altair would have had hydrolox or maybe methalox propellant efficiency.)

FWIW I share your feeling that a "less than Apollo 8" lunar fly-by makes this clearly a "test out the new hardware" mission. It does a pretty good job of that, though!

1- Orion SM performs a large burn, but one where there's no LOC should the burn fail non-catastrophically. So long as RCS propellant remains Orion could limp home from whatever sub-TLI trajectory it had achieved with the failed OME burn.

2- EUS performs multiple burns: ascent, orbit raising after one cool-down, and then its own disposal burn after what could be a much longer cold soak. (In fact if they were daring and the capability were nominally there the disposal burn could be timed to occur just when a lunar orbit insertion burn would have occurred on a lunar orbit mission. Wouldn't that be a confidence builder?!)

3- The scope of what's attempted for ECLSS can be more aggressive because the mission allows the (aforementioned) "ECLSS can fail yet the crew lives" feature.

With all this near-paranoia feeling that the mission must not fail because mission failure would lead to program cancellation maybe the design could be called, "Apollo on meth?"
— 𝐬𝐝𝐒𝐝𝐬 —

Offline brickmack

  • Full Member
  • ****
  • Posts: 975
  • USA
  • Liked: 3273
  • Likes Given: 101
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #19 on: 12/03/2016 03:43 am »
It's a little spooky to see Orion providing its own TLI. Isn't it a bit late in the Orion design effort to be considering this? The requirement would be 443.8 m/s of delta-v I think.

Orion's delta-V is about 1500 m/s (or 4920 ft/s, as NASA prefers to put it), so it does seem feasible, with plenty of margin for mid-course corrections.

The figures I've seen before were about 600 m/s total for insertion and departure burns on a DRO mission with Orion, so even with an additional ~500 m/s for TLI there should be ample margins. Not sure how much that will impact comanifested payload capacity though

Offline sdsds

  • Senior Member
  • *****
  • Posts: 7202
  • “With peace and hope for all mankind.”
  • Seattle
  • Liked: 2050
  • Likes Given: 1962
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #20 on: 12/03/2016 03:56 am »
The figures I've seen before were about 600 m/s total for insertion and departure burns on a DRO mission with Orion

I like the numbers in the attached table, even though its from a "manuscript draft". One of the authors (at least) has had his name on NASA delta-v papers since at least 2009, and so this counts imho as a reliable source.

Page 3: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150019648.pdf
October 21, 2015
Options for Staging Orbits in Cis-Lunar Space
Ryan Whitley
Roland Martinez
— 𝐬𝐝𝐒𝐝𝐬 —

Online TrevorMonty

There is no need for Orion to enter LLO if lander is capable of operating from DRO. The other plus of staging at DRO with more capable lander is it can access all the moon.

Online Steven Pietrobon

  • Member
  • Senior Member
  • *****
  • Posts: 39218
  • Adelaide, Australia
    • Steven Pietrobon's Space Archive
  • Liked: 32738
  • Likes Given: 8192
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #22 on: 12/03/2016 05:31 am »
But then I had a numerical think about radiation doses during multiple passes through the van Allen Belts once before, in the context of multi-pass aerobraking.  To make a long story short, if you have a look at the last attachment to this post, you'll see that the crew of Apollo 13, which made two passes through both van Allen Belts and, like the proposed EM-2 baseline mission, didn't spent a lot of time near the moon, got skin average doses of 2.4 mGy (1 rad = 0.01 Gy).  Even if you assume that dose came entirely from the van Allen Belts, which, of course, it didn't, then scaling the Apollo 13 results to EM-2's six passes gives a total dose of 7.2 mGy.  That's not a lot:  the Apollo 14 crew, for example, got 11.4 mGy.

Thanks for that information! I thought going through the radiation belts was much more hazardous.
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline hektor

  • Senior Member
  • *****
  • Posts: 2706
  • Liked: 1193
  • Likes Given: 54
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #23 on: 12/03/2016 07:01 am »
Europe Takes Off for Space

Quote
Following successes and agreements on the Ariane 6 programme, Airbus Defence and Space is particularly pleased by the ESA space ministers’ commitment to manned space activities, notably their green light for ESA to start working on a second European Service Module for the Orion exploration programme. This European contribution will provide the future US-manned capsules Orion with power and propulsion. Airbus is already prime contractor of the first European Service Module for NASA’s Orion spacecraft. The first un-crewed mission, Exploration Mission-1, will be launched in 2018, followed by the first crewed mission to be launched in 2021.

Offline Proponent

  • Senior Member
  • *****
  • Posts: 7277
  • Liked: 2782
  • Likes Given: 1462
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #24 on: 12/03/2016 10:22 am »
It is probably more accurate to say that in the Constellation architecture the task of lunar orbit insertion was assigned to the Altair lander's propulsion budget rather than the Orion SM propulsion budget. (That was because Altair would have had hydrolox or maybe methalox propellant efficiency.)

I can't help but wonder whether a significant driving factor might have been the desire to justify Ares I: Orion had to be light enough that Ares I could be used to lift it to LEO.

Offline Proponent

  • Senior Member
  • *****
  • Posts: 7277
  • Liked: 2782
  • Likes Given: 1462
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #25 on: 12/03/2016 10:30 am »
Although the notion for a mere lunar flyby feels like a cheap cop-out, I can respect one point of it: the loiter in high Earth orbit.  Wasn't there a notion years ago that, during the early flights of Orion, that it was considered wise to check the vehicle out first in an Earth orbit before pushing all the way to the Moon?  It feels like a reflection back to that, which is wise given the uncertainties there are for Orion, especially the ESM and the EUS.

Yes, and that still seems to be the plan.

Quote
If anything frustrates me aside from delays, I'd say it's the inability to decide what orbit or otherwise where in Cis-Lunar space.  One year it's Lagrange points, another it's Distant Retrograde Orbit, and now this 'Near Rectilinear Orbit' stuff?  Pick a damn orbit for crying out loud!

I share your frustration.  I think this situation is the natural consequence of politicians telling the engineers what hardware to build, and then compounding the problem by being unwilling to fork over adequate funding for the hardware they've insisted be built.

Offline Coastal Ron

  • Senior Member
  • *****
  • Posts: 8862
  • I live... along the coast
  • Liked: 10199
  • Likes Given: 11934
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #26 on: 12/03/2016 03:28 pm »
Although the notion for a mere lunar flyby feels like a cheap cop-out, I can respect one point of it: the loiter in high Earth orbit.  Wasn't there a notion years ago that, during the early flights of Orion, that it was considered wise to check the vehicle out first in an Earth orbit before pushing all the way to the Moon?  It feels like a reflection back to that, which is wise given the uncertainties there are for Orion, especially the ESM and the EUS.

Yes, and that still seems to be the plan.

NASA is trying to pack a lot into this mission, and no doubt that is due to the parallel development of the SLS and the Orion.

If the Orion were being developed without a companion launcher, and just used an existing one, then we'd likely be seeing checkout flights that stayed in Earth orbit, potentially for the full duration of the Orion ECLSS (i.e. ~3 weeks).  Because the majority of items to test on the Orion, except for the heatshield, are not dependent on distance from the Earth, but duration in space.

But the only vehicle Orion is allowed to use is the SLS, and it too needs to be tested, along with the Exploration Upper Stage (EUS), and not only is funding tight but the SLS is very expensive.  So expensive that NASA has to do these combined tests.

So while having a set budget is good, having a transportation so expensive that you can only fly it once per year is not good...
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline Proponent

  • Senior Member
  • *****
  • Posts: 7277
  • Liked: 2782
  • Likes Given: 1462
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #27 on: 12/04/2016 12:46 pm »
Orion's delta-V is about 1500 m/s (or 4920 ft/s, as NASA prefers to put it), so it does seem feasible, with plenty of margin for mid-course corrections.

The figures I've seen before were about 600 m/s total for insertion and departure burns on a DRO mission with Orion, so even with an additional ~500 m/s for TLI there should be ample margins. Not sure how much that will impact comanifested payload capacity though

So, could it be that basically the plan for EM-2 has not changed?  In other words, NASA still wants to send the crew to some sort of lunar orbit, but is now leaving itself a little more wiggle room by redefining the DRO portion of the mission as an optional extra?

Offline redliox

  • Senior Member
  • *****
  • Posts: 2539
  • Illinois USA
  • Liked: 683
  • Likes Given: 97
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #28 on: 12/04/2016 02:01 pm »
If anything frustrates me aside from delays, I'd say it's the inability to decide what orbit or otherwise where in Cis-Lunar space.  One year it's Lagrange points, another it's Distant Retrograde Orbit, and now this 'Near Rectilinear Orbit' stuff?  Pick a damn orbit for crying out loud!

I share your frustration.  I think this situation is the natural consequence of politicians telling the engineers what hardware to build, and then compounding the problem by being unwilling to fork over adequate funding for the hardware they've insisted be built.

Wouldn't be surprised; but I haven't really seen a proper breakdown of these options aside from the delta-v requirements of the Lagrange points.  The only orbit that seems to have a clear-cut function would be the L2 Halo orbit, which is good for staging for Mars and far side operations.

Extreme calculus isn't my forte, but I can understand how elliptical orbits around Luna would be heavily influenced by the Earth's gravity at apoapsis. The Earth essentially counteracts the lumps in the lunar crust which are quick to bring down a low circular orbit over time.  Beyond that I don't know how one orbit is superior to another without a d-v chart in front of me, and even without one it feels like the engineers are grasping at straws.

At face value, all these various lunar orbits seem arbitrary.
"Let the trails lead where they may, I will follow."
-Tigatron

Offline sdsds

  • Senior Member
  • *****
  • Posts: 7202
  • “With peace and hope for all mankind.”
  • Seattle
  • Liked: 2050
  • Likes Given: 1962
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #29 on: 12/04/2016 07:06 pm »
You are right: the high lunar orbits are all pretty much the same. The spacecraft is floating around vaguely in the vicinity of the Moon, without ever getting very close to it. A good way to think about them is that they are really just orbits around the Earth much like the orbit of the Moon around the Earth, except the presence of the Moon perturbs them somewhat.

There's nothing "there" at any of them; they are all just variations on "nowhere." That makes it difficult to get very excited about any them, and I think the NASA public affairs people are aware of that problem.

Sadly, one way they do vary that is easy to understand is that some of them would take astronauts further from Earth than any human has ever before traveled. Is that important in some scientific or engineer way? Well, no. But it might be something the kids can get excited about!

;)
— 𝐬𝐝𝐒𝐝𝐬 —

Offline muomega0

  • Full Member
  • ****
  • Posts: 862
  • Liked: 70
  • Likes Given: 1
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #30 on: 12/04/2016 07:29 pm »
Both of your posts are just quite silly and incorrect.

You are right: the high lunar orbits are all pretty much the same. The spacecraft is floating around vaguely in the vicinity of the Moon, without ever getting very close to it. A good way to think about them is that they are really just orbits around the Earth much like the orbit of the Moon around the Earth, except the presence of the Moon perturbs them somewhat.

There's nothing "there" at any of them; they are all just variations on "nowhere." That makes it difficult to get very excited about any them, and I think the NASA public affairs people are aware of that problem.

Sadly, one way they do vary that is easy to understand is that some of them would take astronauts further from Earth than any human has ever before traveled. Is that important in some scientific or engineer way? Well, no. But it might be something the kids can get excited about!

Orbits matter quite a bit.

The propellant mass and overall mass of the CEV would go way down if L2 rendezvous would be selected rather than lunar-orbit rendezvous.  It would also make the CEV compatible with future Mars missions (both high-thrust and low-thrust) that would depart from L2. 

For a trip to and from L1, the CEV will need about 700 m/s to get in and out of L1:  1400 m/s.  For a trip to and from L2 using lunar powered swingbys, the CEV would only need about 330 m/s each time: ~700 m/s.

The penalties to the lunar surface are quite small as well.  You will be hard pressed to find a better staging point than L2.

Offline sdsds

  • Senior Member
  • *****
  • Posts: 7202
  • “With peace and hope for all mankind.”
  • Seattle
  • Liked: 2050
  • Likes Given: 1962
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #31 on: 12/04/2016 11:51 pm »
I do appreciate what Sorensen wrote back in 2006 regarding CEV design objectives. A decade has passed since then. CEV (along with CLV and CaLV) were flat out cancelled; MPCV was created. It "turned out" the same Orion which had been under development for CEV was "discovered" to be the ideal basis from which to create MPCV. If you understand that last sentence you understand a lot about how NASA works!

And this is a thread about NASA and SLS and Orion and the constraints under which the EM-2 mission will be conducted. If it were about exploration under ideal circumstances or by some other agency or entity I too would be a super-big fan of trajectories in the vicinity of EML2.

In 2012 Gerstenmaier wrote a memo about the advantages of an EML2 waypoint station, based on a briefing he received from John Shannon. Since Gerst is now Associate Administrator for Human Exploration and Operations I think it is fair to say NASA leadership understands the points Sorensen made back in 2006.

Do orbits matter quite a bit? Of course they do! But what works for an engineer isn't necessarily what works for a bureaucrat, or for a politician.
— 𝐬𝐝𝐒𝐝𝐬 —

Offline sdsds

  • Senior Member
  • *****
  • Posts: 7202
  • “With peace and hope for all mankind.”
  • Seattle
  • Liked: 2050
  • Likes Given: 1962
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #32 on: 12/06/2016 08:00 am »
@jongoff: I just read your blog post, "Lunar Orbital Facility Location Options," at:
http://selenianboondocks.com/2016/04/lunar-orbital-facility-location-options/

It makes excellent reading in the context of this thread!

I'm curious what your astrogator friends say about the cost (delta-v, delta-t) of moving between an NRO and an EML2 halo. (Or what anyone else's astrogator friends say about it!)

If the NRO is (as one of the charts you show seems to indicate) essentially a lunar orbit with perilune of 2,000 km and apolune of 75,000 km the apolune velocity is something like 77 m/s. The circular orbital velocity at that distance is 253 m/s, So the cost to head off from there towards just about anywhere in cislunar space would max out at something like 77 + 253 = 330 m/s.

And can't a careful insertion into an EML2 halo orbit be almost free, given enough time?
— 𝐬𝐝𝐒𝐝𝐬 —

Offline redliox

  • Senior Member
  • *****
  • Posts: 2539
  • Illinois USA
  • Liked: 683
  • Likes Given: 97
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #33 on: 12/06/2016 10:42 pm »
@jongoff: I just read your blog post, "Lunar Orbital Facility Location Options," at:
http://selenianboondocks.com/2016/04/lunar-orbital-facility-location-options/

It makes excellent reading in the context of this thread!

I'm curious what your astrogator friends say about the cost (delta-v, delta-t) of moving between an NRO and an EML2 halo. (Or what anyone else's astrogator friends say about it!)

If the NRO is (as one of the charts you show seems to indicate) essentially a lunar orbit with perilune of 2,000 km and apolune of 75,000 km the apolune velocity is something like 77 m/s. The circular orbital velocity at that distance is 253 m/s, So the cost to head off from there towards just about anywhere in cislunar space would max out at something like 77 + 253 = 330 m/s.

And can't a careful insertion into an EML2 halo orbit be almost free, given enough time?

Considering how many lunar orbits there are, perhaps it's time to make a thread specifically on them in the Moon discussions.  That way things can return to specifically focusing on EM-2 here.
"Let the trails lead where they may, I will follow."
-Tigatron

Offline jongoff

  • Recovering Rocket Plumber/Space Entrepreneur
  • Senior Member
  • *****
  • Posts: 6807
  • Lafayette/Broomfield, CO
  • Liked: 3987
  • Likes Given: 1684
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #34 on: 12/07/2016 04:06 am »
@jongoff: I just read your blog post, "Lunar Orbital Facility Location Options," at:
http://selenianboondocks.com/2016/04/lunar-orbital-facility-location-options/

It makes excellent reading in the context of this thread!

I'm curious what your astrogator friends say about the cost (delta-v, delta-t) of moving between an NRO and an EML2 halo. (Or what anyone else's astrogator friends say about it!)

If the NRO is (as one of the charts you show seems to indicate) essentially a lunar orbit with perilune of 2,000 km and apolune of 75,000 km the apolune velocity is something like 77 m/s. The circular orbital velocity at that distance is 253 m/s, So the cost to head off from there towards just about anywhere in cislunar space would max out at something like 77 + 253 = 330 m/s.

And can't a careful insertion into an EML2 halo orbit be almost free, given enough time?

I'll ask. My guess is that you can move between NROs and EML2 for very low propellant costs, if you're willing to take a lot of time. Orbits like those often have Weak-Stability Boundary tricks you can play. No guarantees on a quick reply though. I'm in proposal/final report writing hell for the rest of the week.

~Jon

Offline jongoff

  • Recovering Rocket Plumber/Space Entrepreneur
  • Senior Member
  • *****
  • Posts: 6807
  • Lafayette/Broomfield, CO
  • Liked: 3987
  • Likes Given: 1684
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #35 on: 12/07/2016 04:17 am »
@jongoff: I just read your blog post, "Lunar Orbital Facility Location Options," at:
http://selenianboondocks.com/2016/04/lunar-orbital-facility-location-options/

It makes excellent reading in the context of this thread!

I'm curious what your astrogator friends say about the cost (delta-v, delta-t) of moving between an NRO and an EML2 halo. (Or what anyone else's astrogator friends say about it!)

If the NRO is (as one of the charts you show seems to indicate) essentially a lunar orbit with perilune of 2,000 km and apolune of 75,000 km the apolune velocity is something like 77 m/s. The circular orbital velocity at that distance is 253 m/s, So the cost to head off from there towards just about anywhere in cislunar space would max out at something like 77 + 253 = 330 m/s.

And can't a careful insertion into an EML2 halo orbit be almost free, given enough time?

I'll ask. My guess is that you can move between NROs and EML2 for very low propellant costs, if you're willing to take a lot of time. Orbits like those often have Weak-Stability Boundary tricks you can play. No guarantees on a quick reply though. I'm in proposal/final report writing hell for the rest of the week.

~Jon

My astrogator friend is apparently finishing a paper he'll be presenting on this very topic next month. So we may have to sit tight till the paper is published, but you should have a *very* thorough answer once he's presented.

~Jon

Offline redliox

  • Senior Member
  • *****
  • Posts: 2539
  • Illinois USA
  • Liked: 683
  • Likes Given: 97
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #36 on: 12/07/2016 04:27 am »
I put up a thread to discuss orbits and the use around the Moon here:
https://forum.nasaspaceflight.com/index.php?topic=41784.0

As far as orbits, for EM-2 I am going to guess NASA is going to stay on the cautious side and downplay it as purely a test primarily in high Earth orbit with the simple lunar flyby partially for cheesecake.  The real question is, afterwards, what orbits will Orions fly...and even furthermore what orbit a Deep Space Habitat/Lunar Space Station would occupy.  The lower or more extreme the orbit, the less useful to Mars it becomes, so more solid decisions will need to be made on whether a habitat around the Moon serves the cause for Mars in the long-term.
"Let the trails lead where they may, I will follow."
-Tigatron

Offline sdsds

  • Senior Member
  • *****
  • Posts: 7202
  • “With peace and hope for all mankind.”
  • Seattle
  • Liked: 2050
  • Likes Given: 1962
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #37 on: 12/07/2016 06:44 am »
I put up a thread to discuss orbits and the use around the Moon here:
https://forum.nasaspaceflight.com/index.php?topic=41784.0

[...] The real question is, afterwards, what orbits will Orions fly...and even furthermore what orbit a Deep Space Habitat/Lunar Space Station would occupy.  The lower or more extreme the orbit, the less useful to Mars it becomes, so more solid decisions will need to be made on whether a habitat around the Moon serves the cause for Mars in the long-term.

Yeah, you're right. All that discussion of possibilities beyond EM-2 belong in some other thread.

Quote
As far as orbits, for EM-2 I am going to guess NASA is going to stay on the cautious side and downplay it as purely a test primarily in high Earth orbit with the simple lunar flyby partially for cheesecake. 

I think the question they have to ask for EM-2 is, "How will they convince anyone the mission was worthwhile?" They will have tested the heat shield on EM-1. What gets accomplished leaving LEO on EM-2 that couldn't be accomplished while remaining in LEO? I tried to enthusiastically list the big points up-thread:
[...] makes this clearly a "test out the new hardware" mission.[,,,]

I don't think it convinced anyone....
— 𝐬𝐝𝐒𝐝𝐬 —

Online TrevorMonty

Just because NASA picks a particular orbit for DSH doesn't mean it is stuck there forever. With electric propulsion and a few months the DSH can move to another orbit eg from NRO to EML2.

Offline sdsds

  • Senior Member
  • *****
  • Posts: 7202
  • “With peace and hope for all mankind.”
  • Seattle
  • Liked: 2050
  • Likes Given: 1962
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #39 on: 12/07/2016 11:31 am »
I seem to have erred in my delta-v calculation for the Orion burn in what Chris Gebhardt calls "EM-2 Option 2: Hybrid." In this scenario the EUS leaves Orion in an Earth orbit at 391 x 71333 km and Orion does its own TLI.

From LEO the delta-v required for TLI is quite close to the delta-v required for escape. Not so in this case! Reaching escape would require 443.84 m/s. But just reaching the altitude at which the Moon orbits the Earth would require only 351.05 m/s.

That's a difference that might actually make a difference, as they say.

« Last Edit: 12/07/2016 11:32 am by sdsds »
— 𝐬𝐝𝐒𝐝𝐬 —

Offline sdsds

  • Senior Member
  • *****
  • Posts: 7202
  • “With peace and hope for all mankind.”
  • Seattle
  • Liked: 2050
  • Likes Given: 1962
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #40 on: 12/09/2016 05:43 am »
In the multi-translunar injection mission profile that now seems to be the plan of record for EM-2 has anything been said about the inclinations of the orbits with respect to the plane of the Moon's orbit around the Earth?

Looking closely at the diagram that accompanied the Dec 1 announcement (https://www.nasa.gov/feature/nasa-s-first-flight-with-crew-will-mark-important-step-on-journey-to-mars) it may intentionally show an "over/under" trajectory rather than a coplanar one.

Getting some velocity in the z-axis direction would let Orion pass over more polar regions of the Moon. And it can do that without compromising the "free return" property of the trajectory, so it doesn't reduce crew safety.
— 𝐬𝐝𝐒𝐝𝐬 —

Offline sdsds

  • Senior Member
  • *****
  • Posts: 7202
  • “With peace and hope for all mankind.”
  • Seattle
  • Liked: 2050
  • Likes Given: 1962
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #41 on: 12/09/2016 10:27 am »
I'll trust your judgement about what is an option for EM-2.

But note that for Apollo all TLI impulse was provided while in LEO reached from KSC. For EM-2 only the SLS portion of the TLI impulse must be provided in that kind of orbit.

I'm not saying NASA plans to take advantage of the first Orion apogee (71333 km) to perform a maneuver. I have no idea what NASA plans. But I think Orion could do that and get itself onto a translunar trajectory out of the plane into which SLS delivered it.

And then there's yet another possibility. The Chinese have published (in the the AIAA  Journal of Guidance, Control, and Dynamics) some research on what they call, "Multi Segment Lunar Free-Return Trajectories." In their scheme each trajectory segment is a free return. But they perform a maneuver days after TLI. (It's sort of like where some Apollo flights departed from free return.) I believe that approach might reduce the delta-t and perilune distance penalties.

LOL. Maybe I should write NASA a letter and tell them how to plan this mission!
— 𝐬𝐝𝐒𝐝𝐬 —

Offline Proponent

  • Senior Member
  • *****
  • Posts: 7277
  • Liked: 2782
  • Likes Given: 1462
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #42 on: 12/09/2016 11:44 am »
Sorry, sdsds, shortly after I made the post which I suspect your post immediately above addresses, I decided it fit better here (we seem to be discussing something similar in two places at once).  If I had realized you'd already replied, I'd have left my post where it was.

I'll trust your judgement about what is an option for EM-2.

Please don't -- I'm just guessing!

Quote
But note that for Apollo all TLI impulse was provided while in LEO reached from KSC. For EM-2 only the SLS portion of the TLI impulse must be provided in that kind of orbit.

That's true -- with such a high apogee, Orion could make a substantial plane change with low delta-V.  NASA might still worry about the increased trip time.

Quote
And then there's yet another possibility. The Chinese have published (in the the AIAA  Journal of Guidance, Control, and Dynamics) some research on what they call, "Multi Segment Lunar Free-Return Trajectories." In their scheme each trajectory segment is a free return. But they perform a maneuver days after TLI. (It's sort of like where some Apollo flights departed from free return.) I believe that approach might reduce the delta-t and perilune distance penalties.

Thanks!  Google Scholar turns up a link the full text of the paper, which I hope to read shortly.
« Last Edit: 12/09/2016 12:02 pm by Proponent »

Offline Khadgars

  • Full Member
  • ****
  • Posts: 1750
  • Orange County, California
  • Liked: 1132
  • Likes Given: 3156
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #43 on: 12/09/2016 03:01 pm »
Please feel free to move this to another thread, but I didn't see any chatter in regards to the PM article below (I know they are not held in high esteem here).

http://www.popularmechanics.com/space/moon-mars/a24206/orion-nasa-space-plan/

It seems to cover material from EM-2 onward that I haven't seen here (perhaps in L2).
« Last Edit: 12/09/2016 03:02 pm by Khadgars »
Evil triumphs when good men do nothing - Thomas Jefferson

Offline sdsds

  • Senior Member
  • *****
  • Posts: 7202
  • “With peace and hope for all mankind.”
  • Seattle
  • Liked: 2050
  • Likes Given: 1962
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #44 on: 12/10/2016 08:33 pm »
It looks like Popular Mechanics is reporting the ideas laid out by the Advanced Concepts Office at Marshall as being the "plan of record." Not sure if that's true... but we can hope!

Or is Popular Mechanics saying something different than what Smitherman said?

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160012094.pdf
— 𝐬𝐝𝐒𝐝𝐬 —

Offline redliox

  • Senior Member
  • *****
  • Posts: 2539
  • Illinois USA
  • Liked: 683
  • Likes Given: 97
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #45 on: 12/11/2016 02:31 pm »
It looks like Popular Mechanics is reporting the ideas laid out by the Advanced Concepts Office at Marshall as being the "plan of record." Not sure if that's true... but we can hope!

Or is Popular Mechanics saying something different than what Smitherman said?

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160012094.pdf

Looking at the hab options considered they favor something sized like the SLS tankage at 8+ meter diameters.
"Let the trails lead where they may, I will follow."
-Tigatron

Offline A_M_Swallow

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 8906
  • South coast of England
  • Liked: 500
  • Likes Given: 223
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #46 on: 12/11/2016 05:47 pm »
It looks like Popular Mechanics is reporting the ideas laid out by the Advanced Concepts Office at Marshall as being the "plan of record." Not sure if that's true... but we can hope!

Or is Popular Mechanics saying something different than what Smitherman said?

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160012094.pdf

Looking at the hab options considered they favor something sized like the SLS tankage at 8+ meter diameters.

Since 8 metres diameter is too wide for rail tunnels it will have to be brought in by barge. The workshop will have to be near a river or the sea shore.

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 37441
  • Cape Canaveral Spaceport
  • Liked: 21451
  • Likes Given: 428
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #47 on: 12/11/2016 06:19 pm »

Since 8 metres diameter is too wide for rail tunnels it will have to be brought in by barge. The workshop will have to be near a river or the sea shore.

Rail tunnels have no bearing on the matter.  The US does not use rail to transport payloads across the country

Online TrevorMonty

The 8m has few issues with it compared to modular approach. Needs a dedicated SLS plus a propulsion module to deliver it to DRO after TLI.
That means one less crew mission. The  modules can share a Orion launch and use Orion to deliver them to DRO.
With modules, the crew start getting benefits from 1st module delivered which would be sooner and cheaper than 8m. Budget cuts could push 8m further out leaving crew missions stuck in Orion. If there are budget cuts after first module is delivered, crew will still be able to do 30-60 missions.


Offline okan170

  • Full Member
  • ****
  • Posts: 1111
  • Los Angeles
  • Liked: 6806
  • Likes Given: 1345
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #49 on: 12/11/2016 06:45 pm »
Looking at the hab options considered they favor something sized like the SLS tankage at 8+ meter diameters.

With that in mind, perhaps the 7.2m version is the most likely, as it won't need the 10m PLF in order to fly without aerodynamic mods.  (Assuming the 8.4m fairing is the only one developed aside from the USA cap)

Offline sdsds

  • Senior Member
  • *****
  • Posts: 7202
  • “With peace and hope for all mankind.”
  • Seattle
  • Liked: 2050
  • Likes Given: 1962
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #50 on: 12/11/2016 08:45 pm »
I hope the large hab is openly competed. Would the RFP likely be timed before or after completion of EM-2? That is, would any lessons learned from EM-2 need to be carried forward into the hab requirements?
— 𝐬𝐝𝐒𝐝𝐬 —

Offline Khadgars

  • Full Member
  • ****
  • Posts: 1750
  • Orange County, California
  • Liked: 1132
  • Likes Given: 3156
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #51 on: 12/14/2016 03:04 pm »
I hope the large hab is openly competed. Would the RFP likely be timed before or after completion of EM-2? That is, would any lessons learned from EM-2 need to be carried forward into the hab requirements?

I would expect an RFP to likely go out sometime after EM-1 to be honest.  This of course, pending political winds.
Evil triumphs when good men do nothing - Thomas Jefferson

Offline wannamoonbase

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 5413
  • Denver, CO
    • U.S. Metric Association
  • Liked: 3112
  • Likes Given: 3862
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #52 on: 12/14/2016 06:55 pm »
I'm disappointed in the timidity in decision making.

Go for the Moon, get into orbit and show some marbles. 

It was possible in 1968, I would hope it's possible 50+ years later.
Wildly optimistic prediction, Superheavy recovery on IFT-4 or IFT-5

Offline TomH

  • Senior Member
  • *****
  • Posts: 2938
  • Vancouver, WA
  • Liked: 1868
  • Likes Given: 909
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #53 on: 12/15/2016 01:59 am »
I'm disappointed in the timidity in decision making.

Go for the Moon, get into orbit and show some marbles. 

It was possible in 1968, I would hope it's possible 50+ years later.

I don't think that's a fair thing to say. In 1968, a budget surge had NASA at 4.5% of the federal budget, and most of that was for the manned deep space program. Today NASA is getting about 0.5% of the federal budget and the manned deep space program is only a fraction of that. It's easy for us to sit back and criticize, but these guys have to be very careful with the limited amount of money they are given.

Offline redliox

  • Senior Member
  • *****
  • Posts: 2539
  • Illinois USA
  • Liked: 683
  • Likes Given: 97
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #54 on: 12/15/2016 02:55 am »
I'm disappointed in the timidity in decision making.

Go for the Moon, get into orbit and show some marbles. 

It was possible in 1968, I would hope it's possible 50+ years later.

I don't think that's a fair thing to say. In 1968, a budget surge had NASA at 4.5% of the federal budget, and most of that was for the manned deep space program. Today NASA is getting about 0.5% of the federal budget and the manned deep space program is only a fraction of that. It's easy for us to sit back and criticize, but these guys have to be very careful with the limited amount of money they are given.

Sadly yes.  The Apollo effort amounted to an expensive political gesture; literally "Mooning" the Soviets.  And the point about the budget brings home a further point: NASA had access to nine times its current budgetary resources so it's little wonder both the '80s SEI or the 2000s Constellation efforts floundered.

For the foreseeable future NASA circling the moon is the best it can do although there are some options.
« Last Edit: 12/15/2016 02:56 am by redliox »
"Let the trails lead where they may, I will follow."
-Tigatron

Offline Proponent

  • Senior Member
  • *****
  • Posts: 7277
  • Liked: 2782
  • Likes Given: 1462
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #55 on: 12/15/2016 01:09 pm »
I'm disappointed in the timidity in decision making.-2 f

Go for the Moon, get into orbit and show some marbles. 

It was possible in 1968, I would hope it's possible 50+ years later.

Suppose that before EM-2, SLS flies twice, once for EM-1 and once for Europa Clipper or something like that.  Now compare the flight experience of the relevant systems with that which had occurred by the time Apollo 8 flew, from the top of the stack downward:

SystemApollo 8EM-2
CM52
Heat shield @ hi speed21
SM51
CSM w/crew10
TLI stage71
Launch vehicle22

One could quibble with some of the numbers in the table (e.g., maybe EFT-1 counts as a high-speed heat-shield test, despite the facts that the manufacturing technique has since been changed and the entry speed was somewhat below full trans-lunar speed).  One could point out that, because the state of the art is more advanced now, maybe less flight testing is needed.  But on the whole, EM-2 looks pretty aggressive to me, especially since the NASA-industry team that built Apollo had lots of current experience building manned spacecraft, for more than today's NASA-industry team.  And the latest proposal for EM-2 still seems to include some kind of lunar orbit as an option, if preceding stages of the flight go well.

Basically, I'm just restating what redliox said about the budget being much less than Apollo's:  with less money, less testing is possible.

EDIT:  Fixed two typos -- and corrected spelling of "redliox"!
« Last Edit: 12/15/2016 03:47 pm by Proponent »

Offline redliox

  • Senior Member
  • *****
  • Posts: 2539
  • Illinois USA
  • Liked: 683
  • Likes Given: 97
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #56 on: 12/15/2016 03:07 pm »
Basically, I'm just restating what redilox said about the budget being much less than Apollo's:  with less money, less testing is possible.

Much appreciated  ;)

As far as EM-2 itself is concerned, it still seems possible.  If anything I just see the ESM as the weak point; both in schedule and for the fact it still limits Orion's performance.  It could suffice for some activities, but not directly with lunar landings (as in descending as far as low lunar orbit where that magic happens).  Just as the SLS is going to be upgraded, so should the SM for Orion, whether it be American or European-made.  However I wouldn't expect an upgraded SM until at least EM-5+ due to the budget.
"Let the trails lead where they may, I will follow."
-Tigatron

Offline Khadgars

  • Full Member
  • ****
  • Posts: 1750
  • Orange County, California
  • Liked: 1132
  • Likes Given: 3156
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #57 on: 12/15/2016 04:13 pm »
Basically, I'm just restating what redilox said about the budget being much less than Apollo's:  with less money, less testing is possible.

Much appreciated  ;)

As far as EM-2 itself is concerned, it still seems possible.  If anything I just see the ESM as the weak point; both in schedule and for the fact it still limits Orion's performance.  It could suffice for some activities, but not directly with lunar landings (as in descending as far as low lunar orbit where that magic happens).  Just as the SLS is going to be upgraded, so should the SM for Orion, whether it be American or European-made.  However I wouldn't expect an upgraded SM until at least EM-5+ due to the budget.

I think that is certainly possible.  I also think is likely we'll see something similar to the 5 Seg boosters.  Instead of a whole new design, we'll end up with upgraded versions of the current boosters.  Both of which to happen towards end of 2020's.

Everyone loves to rag on the EM missions, but there is not a single entity currently bending hardware that comes even close to this type of exploration outside of NASA.  SpaceX may get into this game, but that is yet to be seen especially after the financial crunch they're experiencing from the recent failure.

Gods Speed to both of them...
Evil triumphs when good men do nothing - Thomas Jefferson

Offline PahTo

  • Full Member
  • ****
  • Posts: 1698
  • Port Angeles
  • Liked: 271
  • Likes Given: 1194
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #58 on: 12/15/2016 04:46 pm »

I think that is certainly possible.  I also think is likely we'll see something similar to the 5 Seg boosters.  Instead of a whole new design, we'll end up with upgraded versions of the current boosters.  Both of which to happen towards end of 2020's.

Everyone loves to rag on the EM missions, but there is not a single entity currently bending hardware that comes even close to this type of exploration outside of NASA.  SpaceX may get into this game, but that is yet to be seen especially after the financial crunch they're experiencing from the recent failure.

Gods Speed to both of them...

Concur with all.  I've maintained for years, since the earliest word of the 1B variant, that that would be the final edition of this LV.  We *may* see some type of "advanced booster" (read:  HTPB instead of PBAN, perhaps with some type of composite case, or elements of composite with steel case), but that's it.  At that (and not to be all negative) we'll likely only see TWO to six launches of this LV before the program ends.  This from an SLS supporter...
[edit, changed "four" to TWO]
« Last Edit: 12/15/2016 05:05 pm by PahTo »

Offline mike robel

  • Extreme Veteran
  • Senior Member
  • *****
  • Posts: 2304
  • Merritt Island, FL
  • Liked: 369
  • Likes Given: 260
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #59 on: 12/15/2016 05:03 pm »
The telling time will come, unless I missed it, of ATK being told to start making the 1sts set of SRBs after the current casings are exhausted.  Another indicator is the number of SSMEs they have available.  Will they last longer than he casings?

Offline Khadgars

  • Full Member
  • ****
  • Posts: 1750
  • Orange County, California
  • Liked: 1132
  • Likes Given: 3156
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #60 on: 12/15/2016 10:13 pm »
The telling time will come, unless I missed it, of ATK being told to start making the 1sts set of SRBs after the current casings are exhausted.  Another indicator is the number of SSMEs they have available.  Will they last longer than he casings?

My understanding is that there are 16 RS-25 engines to use, which is enough for 4 SLS missions.  I believe there are enough casing (18) for the first 8 SLS missions with 2 casing for spares.  Knowing that, RS-25E production will have to begin at least 4 years before new 5 Segment casings do.

https://www.nasaspaceflight.com/2016/11/orbital-atk-srb-plans-competitiveness-em-1-beyond/
Evil triumphs when good men do nothing - Thomas Jefferson

Offline mike robel

  • Extreme Veteran
  • Senior Member
  • *****
  • Posts: 2304
  • Merritt Island, FL
  • Liked: 369
  • Likes Given: 260
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #61 on: 12/15/2016 10:39 pm »
Thanks for that, so RS-25s are the thing to watch for...I stand corrected.

Offline brickmack

  • Full Member
  • ****
  • Posts: 975
  • USA
  • Liked: 3273
  • Likes Given: 101
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #62 on: 12/16/2016 12:24 am »
Note that the new RS-25Es aren't expected to be built until 2027. 4 flights in 9 years, assuming no delays in production restart.

Offline TomH

  • Senior Member
  • *****
  • Posts: 2938
  • Vancouver, WA
  • Liked: 1868
  • Likes Given: 909
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #63 on: 12/16/2016 12:55 am »
Note that the new RS-25Es aren't expected to be built until 2027. 4 flights in 9 years, assuming no delays in production restart.

Thinking along that time line, assuming that ITS does eventually fly, that will certainly be the death knell of SLS and Orion. Favoritism aside, with no bashing, that's just reality.

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 39270
  • Minnesota
  • Liked: 25240
  • Likes Given: 12115
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #64 on: 12/16/2016 01:29 am »
Same goes for New Armstrong and its lander thing. Yeah, 2027 is quite a long ways out... That's 3 presidential terms away.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline sdsds

  • Senior Member
  • *****
  • Posts: 7202
  • “With peace and hope for all mankind.”
  • Seattle
  • Liked: 2050
  • Likes Given: 1962
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #65 on: 12/16/2016 04:21 am »
Can you guys tie that thought back into EM-2 flight path options? Should those assumptions about non-NASA capabilities and the potential demise of SLS/Orion play into the orbit selection decision?
— 𝐬𝐝𝐒𝐝𝐬 —

Online oldAtlas_Eguy

  • Senior Member
  • *****
  • Posts: 5305
  • Florida
  • Liked: 5005
  • Likes Given: 1444
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #66 on: 12/16/2016 02:52 pm »
Because of the possible commercial competitors going through development and testing at the time of EM-2, SLS/Orion needs to prove out the full set of capabilities to show it is ready for any mission design that fits within the SLS/Orion systems capabilities box.

The one capability that impacts on flight path design of EM-2 is mission duration for the Orion. The flight path needs to be able to be shortened if problems with the mission duration capabilities are found.

If the mission duration capability is not tested then a latter flight will have to test it and have the flight path abort for shortened mission duration. Meaning the Orion is not ready for any mission but still requires more testing.

The end item is that hopefully the SLS or SLS/Orion by 2027 has conducted 3 operational flights. Some combination of the Europa missions and Orion missions.

Offline Khadgars

  • Full Member
  • ****
  • Posts: 1750
  • Orange County, California
  • Liked: 1132
  • Likes Given: 3156
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #67 on: 12/16/2016 03:25 pm »
Note that the new RS-25Es aren't expected to be built until 2027. 4 flights in 9 years, assuming no delays in production restart.

I don't believe that this still holds true.  The most recent EM mission schedule has at least 8 missions by 2029, which would necessitate an earlier production start to RS-25E.
Evil triumphs when good men do nothing - Thomas Jefferson

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 39270
  • Minnesota
  • Liked: 25240
  • Likes Given: 12115
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #68 on: 12/16/2016 04:50 pm »
Note that the new RS-25Es aren't expected to be built until 2027. 4 flights in 9 years, assuming no delays in production restart.

I don't believe that this still holds true.  The most recent EM mission schedule has at least 8 missions by 2029, which would necessitate an earlier production start to RS-25E.
Realistically, the 4th would be 2025 at earliest and 2027 would be the fifth, which would necessitate RS25 production. But of course you'd need to start production several years earlier.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Khadgars

  • Full Member
  • ****
  • Posts: 1750
  • Orange County, California
  • Liked: 1132
  • Likes Given: 3156
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #69 on: 12/16/2016 05:28 pm »
Note that the new RS-25Es aren't expected to be built until 2027. 4 flights in 9 years, assuming no delays in production restart.

I don't believe that this still holds true.  The most recent EM mission schedule has at least 8 missions by 2029, which would necessitate an earlier production start to RS-25E.
Realistically, the 4th would be 2025 at earliest and 2027 would be the fifth, which would necessitate RS25 production. But of course you'd need to start production several years earlier.

Not necessarily.

Quote
"After its maiden flight with a pilot in tow, NASA hopes to begin annual flights to the lunar orbit starting in 2023. All but one of the eight planned missions in NASA's latest flight manifest will be dedicated to the assembly of the mini-International Space Station in lunar orbit. Various pieces of the future habitat will be hitchhiking on each Orion flight."

EM-1 - 2018
EM-2 - 2021
EM-3 - 2023
EM-4 - 2024
__________
EM-5 - 2025
EM-6 - 2026
EM-7 - 2027
EM-8 - 2028
EM-9 - 2029

I suspect we will see production of RS-25E much earlier than you are proposing as NASA is looking at for at least one mission per year.
« Last Edit: 12/16/2016 05:29 pm by Khadgars »
Evil triumphs when good men do nothing - Thomas Jefferson

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 39270
  • Minnesota
  • Liked: 25240
  • Likes Given: 12115
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #70 on: 12/16/2016 06:06 pm »
I said realistically. I'd bet hard cash EM2 isn't launching until 2023 at earliest, then launches every two years after that is most realistic. Which means you can push off RS25 production for several more years.

NASA "looking at" something and NASA realistically doing something are two different things.
« Last Edit: 12/16/2016 06:07 pm by Robotbeat »
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Khadgars

  • Full Member
  • ****
  • Posts: 1750
  • Orange County, California
  • Liked: 1132
  • Likes Given: 3156
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #71 on: 12/16/2016 06:27 pm »
Considering NASA's own safe cadence is one flight per year, I would disagree with that assessment.  We shall see.
Evil triumphs when good men do nothing - Thomas Jefferson

Offline okan170

  • Full Member
  • ****
  • Posts: 1111
  • Los Angeles
  • Liked: 6806
  • Likes Given: 1345
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #72 on: 12/16/2016 06:39 pm »
I said realistically. I'd bet hard cash EM2 isn't launching until 2023 at earliest, then launches every two years after that is most realistic. Which means you can push off RS25 production for several more years.

NASA "looking at" something and NASA realistically doing something are two different things.

2023 was the date if ESA decided not to provide the EM-2 SM.

https://forum.nasaspaceflight.com/index.php?topic=41649.msg1614880#msg1614880

Offline RonM

  • Senior Member
  • *****
  • Posts: 3340
  • Atlanta, Georgia USA
  • Liked: 2231
  • Likes Given: 1584
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #73 on: 12/16/2016 06:40 pm »
NASA states they are planning for one flight per year starting with EM-2. That's what we should be discussing, but in a different thread. This thread is about EM-2 options.

Offline sdsds

  • Senior Member
  • *****
  • Posts: 7202
  • “With peace and hope for all mankind.”
  • Seattle
  • Liked: 2050
  • Likes Given: 1962
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #74 on: 12/16/2016 09:14 pm »
The one capability that impacts on flight path design of EM-2 is mission duration for the Orion. The flight path needs to be able to be shortened if problems with the mission duration capabilities are found.

That's a good observation. A trajectory is better if it allows prompt Earth return with low delta-v, while still allowing a long duration nominal mission.

It wasn't one of the options discussed in the article but I'm curious if a "double figure 8" would rate highly on this metric? Loop around the Moon. Then loop around the Earth, loop around the Moon again, and then return to Earth for reentry.
— 𝐬𝐝𝐒𝐝𝐬 —

Offline Proponent

  • Senior Member
  • *****
  • Posts: 7277
  • Liked: 2782
  • Likes Given: 1462
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #75 on: 12/17/2016 03:50 pm »
You could manage a second pass to the moon's orbit, but I don't see how to arrange to approach the moon on both passes while keeping the mission short enough.

Offline brickmack

  • Full Member
  • ****
  • Posts: 975
  • USA
  • Liked: 3273
  • Likes Given: 101
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #76 on: 12/17/2016 07:26 pm »
Note that the new RS-25Es aren't expected to be built until 2027. 4 flights in 9 years, assuming no delays in production restart.

I don't believe that this still holds true.  The most recent EM mission schedule has at least 8 missions by 2029, which would necessitate an earlier production start to RS-25E.

This information comes from NASAs defense for sole-sourcing RS-25 from Aerojet. That was less than a year ago, and stated that not only would the 5th flight be in 2027, but that they didn't think Aerojet or any other company could deliver the engines faster because restarting the production line will take so long

Offline sdsds

  • Senior Member
  • *****
  • Posts: 7202
  • “With peace and hope for all mankind.”
  • Seattle
  • Liked: 2050
  • Likes Given: 1962
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #77 on: 12/18/2016 07:56 am »
how to arrange to approach the moon on both passes

Hmm. In a non-rotating frame the outbound leg of a standard free return looks just like an elliptical Earth orbit until lunar approach. And the return leg looks like an elliptical Earth orbit too after lunar departure. But the line of apses of those two orbits aren't the same: while we were inside the lunar Hill Sphere doing our swing-by our whole orbital ellipse got twisted around.

So on an Earth swing-by <wild waving of hands> the same thing could happen. The line of apses of the approach and departure trajectories could get twisted such that we were once again going to approach the lunar Hill Sphere.

I suppose rather than wildly waving my hands I ought to ... actually do a simulation or something.
— 𝐬𝐝𝐒𝐝𝐬 —

Offline Khadgars

  • Full Member
  • ****
  • Posts: 1750
  • Orange County, California
  • Liked: 1132
  • Likes Given: 3156
Re: NASA examines options and flight paths for SLS EM-2 mission
« Reply #78 on: 12/18/2016 04:00 pm »
Note that the new RS-25Es aren't expected to be built until 2027. 4 flights in 9 years, assuming no delays in production restart.

I don't believe that this still holds true.  The most recent EM mission schedule has at least 8 missions by 2029, which would necessitate an earlier production start to RS-25E.

This information comes from NASAs defense for sole-sourcing RS-25 from Aerojet. That was less than a year ago, and stated that not only would the 5th flight be in 2027, but that they didn't think Aerojet or any other company could deliver the engines faster because restarting the production line will take so long

Not necessarily true.  The contract is for production restart that runs through Sept 30th 2024 that also includes 6 engines

Quote
"“In order to meet SLS Program flight manifest requirements, production of RS-25 flight engines will be concurrent with the engine recertification effort. The number of new flight engine: to be included as part of this action is six (6)"

You are referring to the part in the document that states the 5th set wouldn't be needed until 2027, which imo was due to the uncertainly of the SLS manifest at the time the contract was awarded over a year ago.  That doesn't preclude delivery of RS-25E before 2027 nor does it not allow for additional units to be purchased to meet the needs of a now, more clear SLS manifest. 

To be clear, additional contract(s) for RS-25E will need to be secured to provide clarity and the required capability above what is on the books now. 

Might I suggest we bring this conversation into a new thread for EM-3 onward, as we've gone far OT.

« Last Edit: 12/18/2016 04:20 pm by Khadgars »
Evil triumphs when good men do nothing - Thomas Jefferson

Tags:
 

Advertisement NovaTech
Advertisement Northrop Grumman
Advertisement
Advertisement Margaritaville Beach Resort South Padre Island
Advertisement Brady Kenniston
Advertisement NextSpaceflight
Advertisement Nathan Barker Photography
0