NASA FY 2011 Appropriations - preview

[Bill White]

That's not what I learnt from orbital mechanics. You want departure and arrival for interplanetary missions to have as low a perigee to Earth as possible, not way up there at EML-1 or EML-2.

One advantage of EML assembly for BEO missions is that hardware can be accumulated at the EML over time, using lower delta -v slow boat trajectories from LEO to the EML point. Solar ion is one option however single impulse ballistic trajectories would not require new propulsion technologies.

A Mars departure from EML-2 would also see a double gravity assist, first via lunar fly-by then an Earth fly-by then on to Mars.

Couldn't a returning trip from Mars also employ an Earth fly-by (combined with a touch of aerobraking?) to slow the transit habitat before arrival at EML-2?

[Bill White]

@ David Hop

Nice pictures! :-)

[Hop_David]

Couldn't a returning trip from Mars also employ an Earth fly-by (combined with a touch of aerobraking?) to slow the transit habitat before arrival at EML-2?

Yes. Only .5 km/sec burn and/or aerobraking would suffice to drop the hyperbolic to an eccentric elliptic with an EML1 or 2 apogee. Then a .65  burn to circularize at EML1 -- but this apogee burn can't be aided by aerobraking. I still haven't grokked paths to EML2 so I won't comment on that.

[Steven Pietrobon]

Sure it's slightly more delta-v than from LEO (0.35 km/s), but you get to assemble &/or fuel much closer (in delta-v) to your destination, and have much more frequent departure windows.

How is it more frequent? You're in a 28 day orbit around Earth which means you are restricted to launch in a window of 18 hours every 28 days (assuming you've budgeted for a 10 degree difference in launch angle). In LEO, your launch opportunity is once every 90 minutes over a period of 10 days for the same 10 degree angle.

Steven's chart seems to indicate LEO to Mars surface at 3.9 km/sec?  What is it that I'm not getting here?

That chart is by Zubrin, not by me. The delta-V from LEO to Mars varies with the launch opportunity (due to Mars being in quite an elliptical orbit) and the required transit time and entry speed at Mars. For example, a minimum delta-V of 3.5 km/s is available in 2033 with a 180 day transit and 6.2 km/s entry speed. In 2024 the delta-V is 4.1 km/s for a 180 day transit and 7.8 km/s entry speed. Read the paper Trajectory Options for Human Mars Missions for more information.

To get from EML1 to a circular LEO orbit takes ~4 km/sec. About .7 km/sec to drop and then a 3.2 circularization burn at perigee.

But with no circularization burn, you're moving 10.8 km/sec at perigee, just under escape. From this speed another .5 km/sec suffices for Trans Mars Insertion.

The path from EML1or2 does exploit the Oberth effect and EML1or2 is much, much closer to Mars than LEO.

You're assuming that the Mars hardware appears at EML-1 for free, when in fact the Mars hardware will appear first at LEO. From your figures:

LEO to Mars: 3.6 km/s
LEO to EML-1 to Mars: 3.1+0.65+0.65+0.5 = 4.9 km/s

[Hop_David]

You're assuming that the Mars hardware appears at EML-1 for free,

No.

Reinserting context:

BTW, it has been said, and quite correctly, that once you are docked at EML-2, you are literally halfway to nearly any location in the solar system. It is the perfect location for earth departure and arrival spacecraft on interplanetary missions.

That's not what I learnt from orbital mechanics. You want departure and arrival for interplanetary missions to have as low a perigee to Earth as possible, not way up there at EML-1 or EML-2.

Clongton correctly noted that once you're at EML-1 or 2, you're much closer to nearly any location in the solar system. You differed with this noting perigee burns deep in a gravity well are advantageous for interplanetary trips.

You seemed to be assuming that interplanetary routes from EML1 would do their perigee burns at EML1. This is wrong.

How you get to EML1 is irrelevant to Clongton's assertion. Once again:

BTW, it has been said, and quite correctly, that once you are docked at EML-2, you are literally halfway to nearly any location in the solar system. It is the perfect location for earth departure and arrival spacecraft on interplanetary missions.

Bolded the part you seemed to have missed.

Actually Clongton is underestimating the advantage of EML 1 or 2. Earth's surface is 14 km/sec from Trans Mars Insertion. EML1 or 2 is 1.2 km/sec from Trans Mars Insertion. Given that propellent fraction rises exponentially with delta V budget, I would say EML1 or 2 is 95% of the way there.

As for where propellent and consumables come from? Lunar volatiles are much closer to LEO and EML1 than earth's surface.


Red lines indicate possible one way aerobraking paths that save propellent.

If propellent and consumables come from the moon, you need only loft the dry mass of the MTV from earth's surface. You wouldn't need a 188 tonne to LEO HLV (Ares V). Nor would you need a 130 tonne to LEO HLV (the current pork frenzy). A 70 tonne to LEO HLV would do quite nicely.

[Hop_David]

From Zubrin's presentation to the Augustine Committee.

I call this the Tucson to Omaha by way of Houston fallacy.

[A_M_Swallow]

The map is wrong.  You cannot get from Earth to Luna without going through LEO and near EML1.

[Rabidpanda]

The wikipedia article on delta V budget has some good data.

http://en.wikipedia.org/wiki/Delta-v_budget

LEO to Mars transfer orbit has a delta v requirement of 4.3 km/s.

LEO to EML1 to C3 to Mars transfer orbit has a delta v requirement of 4.51 km/s (3.77+0.14+0.6)

Not that much of a difference.

[Hop_David]

The map is wrong.  You cannot get from Earth to Luna without going through LEO and near EML1.

The intent of the cartoon is to show a Marsbound space ship would not necessarily have to stop at Luna to use lunar propellent.

Lunar propellent is a short distance from LEO. Zubrin's illustration implies you must go to low lunar orbit to get lunar propellent, which would not be the case for some lunar architectures.

However due to your observation I will revise the cartoon.

[Hop_David]

LEO to Mars transfer orbit has a delta v requirement of 4.3 km/s.

LEO to EML1 to C3 to Mars transfer orbit has a delta v requirement of 4.51 km/s (3.77+0.14+0.6)

Not that much of a difference.

If you have a single propellent source, you don't get to break the delta V budget in chunks. Since all your propellent must be lifted on or above the first stage, all the parts must be summed to a total delta V budget. As your total delta V budget rises, your total mass at lift off rises exponentially

Total mass/dry mass = e^(dV/Ve)

This rises exponentially with dV.

There is a story of a Krishna who made a wager with a king over a chess game. Should the king lose he would give Krishna one grain of rice on the 1st square, two grains on the second, four grains on the third and doubling each subsequent square.



Now if your propellent is oxygen and hydrogen, each 3 km/sec is a square on the chess board.

Say you need 9 km/sec to reach orbit and then another 6 km/sec to reach a moon.

With no propellent depots, all the propellent must be carried aboard at lift off. Your delta V budget would be 15 km/sec. Your total mass to dry mass ratio would be 2^5.

Now, given a depot in orbit, that's propellent that doesn't need to be carried at lift off. This breaks the exponent in the rocket equation. Instead of 2^5, you have two legs, one 2^3 and other leg is 2^2.

32 vs 8 and 4.

A propellent source on your chess board square lets you start over with 1 grain of rice.

The object is not to save propellent but to simplify the rocket. As dry mass fraction shrinks, it becomes harder and harder to make the rocket engine and other components light enough. So dry mass must be discarded along the way. This is expendable stages. More stages means more complexity and failure modes.


red lines are possible one way aerobraking paths that save propellent.

As you can see the moon is much closer to LEO than earth. The ships transporting lunar propellent to LEO and EML1 could be much simpler than ships from earth's surface.

Given propellent depots in LEO, this vastly changes interplanetary trips. Instead of a 14 km/sec trip, you have 10 km/sec hop and a 4 km/sec hop.

It's about 4 km/sec from LEO to EML1. It's also about 4 km/sec to Mars. So what's the point in stopping at EML1? If your Mars Transfer Vehicle (MTV) is making a one way trip, there is no point.

However Mars Semi Direct (MSD) calls for an Mars Transfer Vehicle/Earth Return Vehicle (MTV/ERV) that carries earth propellent aboard for the return trip.

From earth's surface it's total delta V budget is around 16 km/sec.

A propellent depot in LEO would make this 10 and 6.

A propellent depot in LEO and EML1 would make it 10, 4 and 3.

A naive person might conclude a 4 km/sec hop and 3 km/sec hop is worse than one 6 km/sec trip. But these two hops give a propellent fraction that enables a much less ambitious ship than a 6 km/sec vehicle.

It is also worth noting the possibility an MTV can load up on consumables as well as propellent at EML1. Air to breathe, water to drink as well as water for radiation shielding. This could be 30 tonnes for the MSD MTV.

[HappyMartian]

....



It is also worth noting the possibility an MTV can load up on consumables as well as propellent at EML1. Air to breathe, water to drink as well as water for radiation shielding. This could be 30 tonnes for the MSD MTV.

Nice job Hop_David! Thank you.

Cheers! 

[psloss]

Draft of an omnibus appropriations bill released by the Senate Appropriations committee:
http://www.appropriations.senate.gov/news.cfm?method=news.view&id=9ac3518e-7e19-4328-bf52-16a6c2a1d333

Summary:
http://www.appropriations.senate.gov/news.cfm?method=news.view&id=00058c70-649a-435f-9b73-85832758a0b1

Still waiting to see whether the Senate takes up this bill or the heavily-marked-up continuing resolution bill that the House passed.

[yg1968]

Draft of an omnibus appropriations bill released by the Senate Appropriations committee:
http://www.appropriations.senate.gov/news.cfm?method=news.view&id=9ac3518e-7e19-4328-bf52-16a6c2a1d333

Summary:
http://www.appropriations.senate.gov/news.cfm?method=news.view&id=00058c70-649a-435f-9b73-85832758a0b1

Still waiting to see whether the Senate takes up this bill or the heavily-marked-up continuing resolution bill that the House passed.

NASA starts at page 184.

[yg1968]

See page 187 of the Senate Onibus FY 11 Appropriation bill which indicates the following:

1 [...]Provided fur-
2 ther, That the initial lift capability for the heavy lift launch
3 vehicle system shall be not less than 130 tons and that
4 the upper stage and other core elements shall be developed
5 simultaneously.

[Orbiter]

I didn't read anything about STS-135.

Orbiter

[Namechange User]

See page 187 of the Senate Onibus FY 11 Appropriation bill which indicates the following:

1 [...]Provided fur-
2 ther, That the initial lift capability for the heavy lift launch
3 vehicle system shall be not less than 130 tons and that
4 the upper stage and other core elements shall be developed
5 simultaneously.

It's kind of a shame they appear to still be pushing 130 tons right out of the gate.

[Namechange User]

I didn't read anything about STS-135.

Orbiter

$825 million for an additional Shuttle flight, if determined to be safe, and for launch infrastructure for the heavy lift rocket;

[Jorge]

I didn't read anything about STS-135.

Orbiter

The omnibus bill also deletes this clause from the full-year CR:

13 ... and $825,000,000 shall
14 be for additional Space Shuttle costs, launch complex de-
15 velopment only for activities at the Kennedy Space Center
16 related to the civil, nondefense launch complex, use at
17 other National Aeronautics and Space Administration
18 flight facilities that are currently scheduled to launch
19 cargo to the International Space Station, and development
20 of ground operations for the heavy lift launch vehicle and
21 the Orion multipurpose crew vehicle

However, the top-line amount for Space Operations ($5,247,900,000) remains the same in both bills. I would assume that line-items not explicitly accounted for would remain "programmable" by NASA provided there are not prohibitions in the Authorization act against it, and that the fact that the Authorization act gives the go-ahead for STS-135 means they can fly it as long as they have the funding to do it.

[yg1968]

I didn't read anything about STS-135.

Orbiter

We can wait for 51D Mascot's comments on this but I don't think that they need to add any additionnal language as long as the overall funding for Space Operations is sufficient, the LON must be added given the wording of the 2010 NASA Authorization bill.

[psloss]

I didn't read anything about STS-135.

It's not mentioned that way, since the already enacted re-authorization mandates the flight but doesn't fund it.  This draft bill and the House bill both fund Space Operations at the same top line of ~$5.2B.  While the House bill specifically allocates $825M for additional Shuttle costs, this draft doesn't, even though that $825M is "there."  That would presumably give NASA (and specifically SOMD) more discretion in terms of how that money might be spent.