Author Topic: NASA examines options and flight paths for SLS EM-2 mission  (Read 22510 times)

Offline sdsds

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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
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Offline 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.

Offline Steven Pietrobon

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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.
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Offline hektor

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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

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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

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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

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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.

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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

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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...
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Offline Proponent

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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

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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.
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Offline sdsds

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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!

;)
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Offline muomega0

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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

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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.
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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?
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Offline redliox

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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.
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Online jongoff

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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

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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

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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.
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Offline sdsds

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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.

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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....
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Offline 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

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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 »
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