NASA SLS/Orion/Payloads

[tater]

Just now, Canopus said:

another advantage for the high orbit given is that supply launches to the gateway can be undertaken by smaller rockets. 

Yeah, but that just supplies the gateway, that mass still has to be taken to the surface if that;s what you are there for. What's the point of DSG, exactly? If the goal is to support lunar surface exploration, then put it in the place best suited for that goal. At the point any landers are available, the supplies that need to be sent will be propellants.

[Canopus]

1 minute ago, tater said:

Yeah, but that just supplies the gateway, that mass still has to be taken to the surface if that;s what you are there for. What's the point of DSG, exactly? If the goal is to support lunar surface exploration, then put it in the place best suited for that goal. At the point any landers are available, the supplies that need to be sent will be propellants.

Then you won‘t have spacecraft that can reach the Gateway. They think a lander can reach from NRHO to the Surface and they thought it can reach the surface from Lunar Lagrange points. No reason to change a practically existing Spacecraft if you can develop a new lander that fills the extra delta v gap later.

[sevenperforce]

Someone ought to make a really detailed subway map showing very clearly the dV cost of various destinations from LEO to cislunar space, specifically with lunar surface architecture in mind.

At present, the default approach for sending anything to cislunar space is to fling it out of LEO with short-lived, high-energy chemical propellants, and then brake it into its destination with expendable stages and storable propellants. It's been that way ever since the first lunar missions. Do we change that? Lunar missions using F9 or FH would not. SLS would not. BFS, obviously, would. New Glenn and Blue Moon may change that; I don't know.

Placement of architecture hardware is wholly dependent on having that subway map clearly identified and knowing how you're going to be getting stuff to the moon.

Designing LOP-G to occupy an orbit designed for a vehicle that was not designed for lunar missions is such nonsense.

EDIT:

One complication of designing such a subway map is that there are numerous paths to a given destination which require more or less dV depending on how many burns you can perform. A three-impulse trajectory can take advantage of gravity wells that a two-impulse trajectory cannot: for example, a two-impulse trajectory will put you in NRHO for around 3.8 km/s past LEO, while a three-impulse trajectory can pull it off with 3.4 km/s. So either you design your map for all possible spacecraft capabilities, which means it rapidly becomes far too large to use, or you design it with your spacecraft's capabilities already in mind, which is putting the cart before the horse at the outset.

Edited April 9, 2018 by sevenperforce

[Tullius]

1 hour ago, tater said:

Wouldn't a low, frozen lunar orbit be preferable for surface missions? While highly elliptical, such orbits have a much lower apolune than the proposed DSG orbit.

Note that the only reason a better lunar orbit is not used by DSG... is that Orion cannot go there.

This pdf provides a few reasons for selecting a NRHO over a low lunar orbit: https://sservi.nasa.gov/wp-content/uploads/ger-downloads/day1/Whitley-LunarSurface-GER3-Workshop-20171130.pdf

In summary: It is not just because Orion cannot go to a lower orbit, but also because it offers a much better place for a lunar orbit space station (less station-keeping fuel needed, very few eclipses, no communication blackout, and less cooling needed), while still offering an acceptable access to the lunar surface.

[tater]

28 minutes ago, Tullius said:

This pdf provides a few reasons for selecting a NRHO over a low lunar orbit: https://sservi.nasa.gov/wp-content/uploads/ger-downloads/day1/Whitley-LunarSurface-GER3-Workshop-20171130.pdf

In summary: It is not just because Orion cannot go to a lower orbit, but also because it offers a much better place for a lunar orbit space station (less station-keeping fuel needed, very few eclipses, no communication blackout, and less cooling needed), while still offering an acceptable access to the lunar surface.

That powerpoint is right as far as it goes, but it does not in fact answer my question. It compares the orbits Orion can go to with LLO, which it cannot go it. I didn't say LLO, I said a frozen lunar orbit. Frozen != LLO. They are highly elliptical, for one.

Note that in the image below the author colorized the key, but it doesn't always match the plots, lol. LLO is the ring almost touching the surface (color seems right), ELO is the right color, PCO and Frozen are swapped color-wise, Frozen is orange.

 

Here they are with some DSG possible orbits:

 

[Tullius]

7 minutes ago, tater said:

That powerpoint is right as far as it goes, but it does not in fact answer my question. It compares the orbits Orion can go to with LLO, which it cannot go it. I didn't say LLO, I said a frozen lunar orbit. Frozen != LLO. They are highly elliptical, for one.

Indeed, I messed that one up.

Googling a bit further, I fund this stackexchange question: https://space.stackexchange.com/questions/23992/why-is-a-near-rectilinear-halo-orbit-proposed-for-lop-g-formerly-known-as-deep , whose first answer references this article by NASA: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150019648.pdf. It provides in particular this table, which I think was already posted in this thread and I couldn't find when I wrote the previous post:

In short, NRHO beats a frozen orbit, except for station keeping, although that is still kept relatively low.

[tater]

Occultation (that table they made is typoed) can be easily dealt with via higher orbiting lunar satellites as relays, so it's a non-issue, IMO.The thermal environment I am unsure of.

[Tullius]

4 minutes ago, tater said:

Occultation (that table they made is typoed) can be easily dealt with via higher orbiting lunar satellites as relays, so it's a non-issue, IMO.The thermal environment I am unsure of.

Is it really worth putting several satellites into a higher lunar orbit just to save on a relatively small amount of station-keeping fuel?

[tater]

13 minutes ago, Tullius said:

Is it really worth putting several satellites into a higher lunar orbit just to save on a relatively small amount of station-keeping fuel?

I was thinking of the total round trip dv to and from the station to the surface, not station keeping at all. Satellites can be cheap. Omni antennae, and throw them in sunsync orbit. These are simple craft, and SLS/Orion is supposed to deliver cubesats to lunar orbit anyway.

Bottom line is that f the goal is the lunar surface, with an orbital base/depot above, the plan should be to optimize that mission design, then build the craft to accomplish that goal. Instead, they have a craft and LV, and then they are trying to make a goal that it can do. It's backwards, IMHO.

 

[DAL59]

[tater]

Doesn't show the differences between the various lunar orbits we are discussing.

Frozen saves maybe a couple hundred m/s from NRHO, but given a reusable lander, it has to carry those ascent props in both directions. I suppose for a given lander design, you would look at what that means in terms of how many refilling runs it takes from Florida. Also, we then end up with loads of empty prop tanks in lunar orbit (used to refill the lander).

A novel lander approach might be one where the ascent tank is separate, and the descent tank is in fact left on the surface with the cargo. Nanoracks is working with ULA to make wet labs out of hydrolox tanks anyway. This would result in leaving a tank on the surface for hab conversion with every run. Think along the lines of ACES/XEUS, so that the tank is large enough to bypass DSG, and simply go to the lunar surface...

[Tullius]

11 minutes ago, tater said:

I was thinking of the total round trip dv to and from the station to the surface, not station keeping at all. Satellites can be cheap.

If the above table can be trusted, a NRHO provides both a faster and cheaper access to the surface than a frozen orbit, all with the advantage that less delta-v is needed to reach it from the Earth.

15 minutes ago, tater said:

Bottom line is that f the goal is the lunar surface, with an orbital base/depot above, the plan should be to optimize that mission design, then build the craft to accomplish that goal. Instead, they have a craft and LV, and then they are trying to make a goal that it can do. It's backwards, IMHO.

Looking at the above table, a NRHO seems to be the most preferable option for doing this, except for a LLO. However, a LLO requires a lot of station-keeping fuel, which is problematic considering the flight-rate of SLS, making a NRHO the second-best option.

The DSG and SLS are of course backwards, but considering the long running time of any crewed program at NASA, it is not surprising that the goals change regularly due to congress and whatnot and NASA then having to make do with whatever they have got. But still, if the only restricting factor in choosing a better lunar orbit were Orions delta-v budget, NASA would certainly have already considered increasing it.

[Canopus]

https://www.nasaspaceflight.com/2018/04/nasa-request-alternative-rs-25s-sls-core-stage-uncontested/

[_Augustus_]

6 hours ago, Canopus said:

https://www.nasaspaceflight.com/2018/04/nasa-request-alternative-rs-25s-sls-core-stage-uncontested/

Solely so they can say "well, we looked for other engines!" - we all know what will win.

[Canopus]

1 minute ago, _Augustus_ said:

Solely so they can say "well, we looked for other engines!" - we all know what will win.

They couldn‘t go for something like BE-4 without redesigning the whole vehicle. This isn‘t KSP after all. So it will have to be the RS-25e or something like it.

[tater]

11 minutes ago, Canopus said:

They couldn‘t go for something like BE-4 without redesigning the whole vehicle. This isn‘t KSP after all. So it will have to be the RS-25e or something like it.

That would require new tanks, RS-25 is hydrolox. Be-3 is for that propellant, but doesn't hit the other specs. There is no other engine extant that can do what they are requiring (match RS-25 as a drop in replacement), so @_Augustus_ is right as far as I can tell.

[Canopus]

9 minutes ago, tater said:

That would require new tanks, RS-25 is hydrolox. Be-3 is for that propellant, but doesn't hit the other specs. There is no other engine extant that can do what they are requiring (match RS-25 as a drop in replacement), so @_Augustus_ is right as far as I can tell.

Thats what i meant. There is no matching hydrolox engine in existence or in development. So it will have to be a further development of RS-25 or a replica engine. Just that @_Augustus_ sounded so cynical when in fact they have to look at replacements once the SSMEs run out. 

[tater]

4 minutes ago, Canopus said:

Thats what i meant. There is no matching hydrolox engine in existence or in development. So it will have to be a further development of RS-25 or a replica engine. Just that @_Augustus_ sounded so cynical when in fact they have to look at replacements once the SSMEs run out. 

The replacement will be the same engine. Likely altered to make it more affordable---altered at vast cost, such that it likely costs just as much or more. (cost plus)

[ment18]

The only remotely similar engines are rd-0120 and rs 68, rd-0120 won't be used for political reasons, and the rs 68 would incur very large payload loss due to terrible Isp and large mass (would work*).  No engine even comes close to meeting their requirements, maybe because those requirements necessitated the most complicated engine ever made.

[sevenperforce]

30 minutes ago, ment18 said:

The only remotely similar engines are rd-0120 and rs 68, rd-0120 won't be used for political reasons, and the rs 68 would incur very large payload loss due to terrible Isp and large mass (would work*).  No engine even comes close to meeting their requirements, maybe because those requirements necessitated the most complicated engine ever made.

Not to mention that the RS-68 has big problems if you try to cluster it.

So what, exactly, have we done here?

• We have leftover rocket bits. Let's build a new rocket that will use those bits!
• Wait, we want to do more with the rocket. Build a newer rocket that will do more!
• Redesign ALL the bits for the bigger rocket!
• This is getting expensive. Let's make it smaller and just focus on using those bits.
• Those bits don't work so well for what we want. Let's just redesign some of the bits.
• We are going to run out of bits. We need to make more bits to fit the rocket we designed to fit the leftover rocket bits we had.

[tater]

Yeah, the "reuse Shuttle parts" bit wasn't thought through. If they change anything about the current engine to make more, then they have to recertify the whole thing, right?

[_Augustus_]

24 minutes ago, tater said:

If they change anything about the current engine to make more, then they have to recertify the whole thing, right?

NASA following their own certification standards? Say what?

[_Augustus_]

Crew on ICPS confirmed.

EUS could be cancelled.

Possibly more test flights, all with ICPS, with unmanned Orion before a crew mission. Seems unlikely.

Edited April 16, 2018 by _Augustus_

[Canopus]

What a bummer. SLS with ICPS is pretty useless.

Edit: is there an updated schedule available anywhere? Because if they are just splitting EM-2 from a combined Block 1b launch into a commercial and a block 1, it wouldn't be that bad.

Edited April 16, 2018 by Canopus

[Ultimate Steve]

So now SLS is NET 2021... And crew is NET 2025... This is just sad...  At least we'll have more than one flight before crew, although at this point crew may not fly...

EDIT:

So not that hopeless after all.

Edited April 16, 2018 by Ultimate Steve