6
$\begingroup$

I was looking around for gravity gradients then got sidetracked by looking at pork-chop plots because they're extremely cool. I'm still struggling to fully understand them, but I did find an interesting one that seems to be talking about the delta-v requirements for a mission to mars in 2354 leaving from Earth in 2353.

enter image description here

Original Link: http://www.projectrho.com/public_html/rocket/images/mission/Mars2353PorkChop.png

It's from projectrho, but I was wondering if anyone could describe more in detail about how, given two dates, you would decide the values for each of the points in the plot? Is it simply calculating the best possible scenario for delta-v budget in terms of a transfer between the two bodies for the provided dates? What types of delta-v does this plot account for: aerobraking, impulsive maneuvers, gravity assists? If you have more specific information about the porkchop plot itself (as in what the specific mission was) I would also like to see that, I found this on google and it led me to this page.

$\endgroup$
3
$\begingroup$

These data points are all variations from the optimal Hohmann Transfer, a specific orbital maneuver to go from circular orbit to circular orbit minimizing DeltaV. A certain alignment of the planets results from a certain departure and arrival date. From the geometry of the situation, different planet alignments have different DeltaV requirements and travel times at minimum DeltaV. The trip can also be sped up by using additional DeltaV.

The tradeoff here can by analogized by a golf swing. If the golf ball is placed ahead of or behind the tee in the path of the golf club, the club won’t be at its maximum velocity at impact and the golf ball won’t go as far. A harder swing can make up for this.

I assume this does not take into account aerobraking or gravity assists, and does include Earth launch and propulsive Mars landing.

Rough DeltaV calculation:

  • Earth Launch to LEO: <10km/s
  • Mars Transfer: <6km/s (plus excess used for speed/suboptimal transfer)
  • Low Mars Orbit velocity: <3.5km/s
  • Additional Propulsive Landing inefficiencies: ~2km/s

Sum: 21.5km/s

$\endgroup$
  • 3
    $\begingroup$ There is no Hohmann transfer from the Earth to Mars. The two planets are not in the same orbital plane, and neither has a circular orbit. $\endgroup$ – David Hammen Jul 3 at 12:50
  • $\begingroup$ @DavidHammen does that explain somewhat the shape of the plot? $\endgroup$ – Magic Octopus Urn Jul 3 at 13:16
  • $\begingroup$ It is so relevant the inclination change maneuver in the context of this mission?. If I am not wrong, the inclination change should be 1.85º only. $\endgroup$ – Julio Jul 5 at 9:58
  • 1
    $\begingroup$ The plane change is somewhat close to a constant DeltaV requirement $\endgroup$ – CourageousPotato Jul 5 at 13:07
  • $\begingroup$ @CourageousPotato No, if you time it right you can pay the plane change price with aerobraking. $\endgroup$ – Loren Pechtel Jul 7 at 2:01

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.