Lunar "X Prize"

[Bob B.]

Feb 25, 2010 0:54:05 GMT -4 ka9q said:

Right, though the exact value depends on the eccentricity of the lunar transfer orbit.

Right, I was just ballparking it based on an Apollo-type trajectory.

I don't remember the apogee of the typical Apollo transfer ellipse but it was somewhat past the moon for this reason.

It varied quite a bit from mission to mission. I don't have the exact numbers, but based on the eccentricities, the apogees appear to be in the range of about 450,000 to 600,000 km.

[Bob B.]

Below is a table I threw together showing a variety of transfers. The only difference between the first and second groups is that the first initiates from 185 km circular LEO and the second initiates from GTO. The TLI Δv is that required for the altitude change only, no plane change is included. I've assumed an Earth-Moon distance of 385,000 km, which is about the mean distance. "@ Arrival" refers to when the satellite reaches the distance of the Moon's orbit. The effect of lunar gravity is neglected; this is a simply two-body calculation.



a = semimajor axis
R_p = perigee radius
R_a = apogee radius
e = eccentricity
TLI = translunar injection
Δv = velocity change
ν = true anomaly
ϕ = flight path angle

[ka9q]

Wow, that really shows the effect, doesn't it? A change in TLI delta V of less than 50 m/sec changes the time of flight by almost a factor of two.

[bazbear]

Feb 22, 2010 5:11:33 GMT -4 ka9q said:

I agree, it's highly unlikely. The prize certainly won't come close to covering the cost.

I was annoyed by all the "go private enterprise, rah rah rah" cheerleading during the Spaceship One demonstration. I have nothing against private individuals and commercial companies going into space, but I thought they were more than a little disingenuous in implying that they were close to providing commercial space services. They really exploited the fact that few laymen understand that the hard part in making low earth orbit isn't the altitude but the velocity. I figured SpaceShip One had only about 3% or 4% of the total energy needed to make even a minimal (exo-atmospheric) earth orbit.

And it was hardly the first time that a rocket built by a commercial company had entered space. Practically every US rocket was built by a commercial company.

Spaceship One was ground breaking only in that it had a human pilot, it was totally civilian, and reached the arbitrary 100 km height deemed internationally to be a suborbital flight. I've heard elsewhere that it had "around 1/20th" the energy needed to reach LEO, so I guess they more or less had the right numbers.

[bazbear]

And thank you all for finally getting around to my post, it took so long for a first reply I thought I might have laid a stinky egg or something. But of course we're all busy doing our earth jobs Some are building satellites, some are cooking Italian food. ;D