Delta V: Low Lunar Orbit to Surface?

Can anyone tell me what the delta V required by a lunar lander / ascent
vehicle is?

http://www.answers.com/topic/delta-v-budget gives 1600 m/s.

http://www.pma.caltech.edu/~chirata/deltav.html also gives 1600m/s.

http://spacecraft.ssl.umd.edu/academ...mech_2003C.pdf
gives 2.132km/s for ascent, and 2.684km/s for descent.

Escape velocity from the moon is 2.38km/s, so IIRC, to lunar orbit
should = 2.38 / sqrt(2) = 1.68km/s.

What do NASA budget and how low is a low lunar orbit?

Thanks

Alex

Alex Terrell wrote:
Can anyone tell me what the delta V required by a lunar lander / ascent
vehicle is?

http://www.answers.com/topic/delta-v-budget gives 1600 m/s.

http://www.pma.caltech.edu/~chirata/deltav.html also gives 1600m/s.

Like you, I got at least 1.68 km/s. That's for a 0 km altitude orbit. An
orbit that'd last a little while would have to higher because the moon's
uneven gravity field would destabilize a low moon orbit.

It puzzles me that they give 1600 m/s. If they're rounding, 1700 m/s is
a better approximation.


--
Hop David
http://clowder.net/hop/index.html

Hop David wrote:
Alex Terrell wrote:
Can anyone tell me what the delta V required by a lunar lander / ascent
vehicle is?
http://www.answers.com/topic/delta-v-budget gives 1600 m/s.
http://www.pma.caltech.edu/~chirata/deltav.html also gives 1600m/s.

Like you, I got at least 1.68 km/s. That's for a 0 km altitude orbit. An
orbit that'd last a little while would have to higher because the moon's
uneven gravity field would destabilize a low moon orbit.

It puzzles me that they give 1600 m/s. If they're rounding, 1700 m/s is
a better approximation.

I commend to you:
http://www.retro.com/employees/gherb...PlusStats.html
aka http://tinyurl.com/2ft8m

(thank you, gods of random capricious alphanum generation)

The above tabulation is from many different tables in the
Apollo By The Numbers book.

max Apollo descent injection burn 214 ft/sec
max LM descent 6813 ft/sec
max LM ascent 6076 ft/sec

Total of maxes is 13,103 ft/sec = 3,995 m/s.

The numbers used in people's CEV proposals are plus or
minus a tiny skosh exactly these values. You can get
a moderately better profile with different thrusts
for the propulsion but not a whole lot. There's a bit
of a description in the trajectories/entry/landing
chapter of Human Spaceflight Mission Analysis and Design.


-george william herbert
/

Thanks.

Any idea how this would change for a polar base? I suspect it would be
minimal change for a direct descent cargo.

However, I've hear that lunar polar orbits are unstable, which might
make leaving the CEV in polar orbit problematic. However, to go from a
pole to an equatorial orbit woud use extra delta-V. How much?

One could park the CEV at L1, but the L1 to moon journey time would be
a day or so.

George William Herbert wrote:
Hop David wrote:

Alex Terrell wrote:

Can anyone tell me what the delta V required by a lunar lander / ascent
vehicle is?
http://www.answers.com/topic/delta-v-budget gives 1600 m/s.
http://www.pma.caltech.edu/~chirata/deltav.html also gives 1600m/s.

Like you, I got at least 1.68 km/s. That's for a 0 km altitude orbit. An
orbit that'd last a little while would have to higher because the moon's
uneven gravity field would destabilize a low moon orbit.

It puzzles me that they give 1600 m/s. If they're rounding, 1700 m/s is
a better approximation.


I commend to you:
http://www.retro.com/employees/gherb...PlusStats.html
aka http://tinyurl.com/2ft8m

(thank you, gods of random capricious alphanum generation)

The above tabulation is from many different tables in the
Apollo By The Numbers book.

max Apollo descent injection burn 214 ft/sec
max LM descent 6813 ft/sec

Which (according to Google's calculator) is 2076.6 m/sec

max LM ascent 6076 ft/sec

Which is 1852 m/sec.

Maybe it's a little higher than the 1680 m/sec figure Alex & I reached
because the low moon orbit is higher than 0 km/sec. Also I'd guess the
ascent and descent burns would have a vertical vector component and thus
gravity drag would steal delta vee for the duration of the burn.


Total of maxes is 13,103 ft/sec = 3,995 m/s.

The numbers used in people's CEV proposals are plus or
minus a tiny skosh exactly these values. You can get
a moderately better profile with different thrusts
for the propulsion but not a whole lot. There's a bit
of a description in the trajectories/entry/landing
chapter of Human Spaceflight Mission Analysis and Design.

By Pranke & Larson? Amazon lists it for $64.75. A little high but it
sounds like a good resource. I might get it.



-george william herbert
/



--
Hop David
http://clowder.net/hop/index.html