Mars Mission Parking Orbit and Delta-V Losses Q&A

[crickmaster]

First post on these forums, hope it is in the right place.  I do apologize if it isn't.

I've been looking at optimum circular parking orbits that would give the lowest delta-V boost for a Hohmann transfer to Mars using the patched conics approximation. 

I've been following the methods in the paper
 "EFFICIENT PLANETARY PARKING ORBITS WITH EXAMPLES FOR MARS"
By Roger W. Luidens and Brent A. Miller
Lewis Research Center

From my calculations, the Earth-departure parking orbit that would give the lowest delta-V boost for the mission is at approximately r= 91940 km, which is pretty high compared to the norm.

Not being familiar with the launch phase of missions, I wanted to know how would a spacecraft get up to that kind of altitude? Would it have a direct ascent to some altitude in LEO before burning again to reach that circular orbit, and hence incurring an extra delta-V, making going to the optimum parking orbit pointless?

Or would it directly ascend to that altitude? If it directly ascended to that altitude, again, would the delta-V losses due to drag be so great that it would negate the savings of the optimum circular parking orbit?  Is there any way for me to estimate what these losses might be?'

If the efficient circular parking orbit is not the way to go, how should I select the parking orbit for the mission?

[deltaV]

Launch vehicles can take far less mass to a 92 Mm circular orbit than to a typical 400 km parking orbit. For example look at Delta IV and Atlas V payload planners guides (available online); IIRC at least one of them gives a graph of performance vs. circular orbit altitude. For best efficiency a parking orbit should have perigee only a few hundred km above the surface of the Earth. Usually a circular LEO parking orbit is used, but sometimes people propose either a highly eccentric parking orbit or a parking orbit at an Earth-Moon Lagrange point.

[Hop_David]

First post on these forums, hope it is in the right place.  I do apologize if it isn't.

I've been looking at optimum circular parking orbits that would give the lowest delta-V boost for a Hohmann transfer to Mars using the patched conics approximation. 

I've been following the methods in the paper
 "EFFICIENT PLANETARY PARKING ORBITS WITH EXAMPLES FOR MARS"
By Roger W. Luidens and Brent A. Miller
Lewis Research Center

From my calculations, the Earth-departure parking orbit that would give the lowest delta-V boost for the mission is at approximately r= 91940 km, which is pretty high compared to the norm.

Not being familiar with the launch phase of missions, I wanted to know how would a spacecraft get up to that kind of altitude? Would it have a direct ascent to some altitude in LEO before burning again to reach that circular orbit, and hence incurring an extra delta-V, making going to the optimum parking orbit pointless?

Or would it directly ascend to that altitude? If it directly ascended to that altitude, again, would the delta-V losses due to drag be so great that it would negate the savings of the optimum circular parking orbit?  Is there any way for me to estimate what these losses might be?'

If the efficient circular parking orbit is not the way to go, how should I select the parking orbit for the mission?

Elliptical orbits, the lower the periaerion and higher the apoaerion, the less delta V it takes to exist Hohmann for Mars capture. Setting periapsis at 200 km and apoapsis at 570,000 km, I get .7 km to exit Hohmann for capture (see attached graphic). Got that from this spreadsheet. Once you have atmosphere grazing periapsis, you can use aerobraking to lower apoapsis and circularize orbit.

However, for any particular elliptical orbit, it's periapsis wouldn't be in the right place when the launch windows come along every 2.14 years.

Dropping from Deimos to to a low periaerion takes .65 km/s. At that periapsis, 1 km/s suffices for insertion to Mars to earth Hohmann. So Deimos is about 1.7 km/s from Hohmann insertion

[crickmaster]

Thank you for your replies.  They have been very helpful.  I've got a follow up question to your posts, what is the advantage of setting the apoapsis at an Earth-Moon lagrange point?  Is any one Earth-Moon lagrange point better than the other?

[Hop_David]

Thank you for your replies.  They have been very helpful.  I've got a follow up question to your posts, what is the advantage of setting the apoapsis at an Earth-Moon lagrange point?  Is any one Earth-Moon lagrange point better than the other?

Here's a delta V map showing some of the numbers.

EML1 has an about 2.4 advantage over LEO, EML2 has an about 2.7 km/s advantage over LEO.