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A launch service request was recently put out for Europa Clipper to do a flyby of Mars on its way to Jupiter. How is that a better trajectory than an EEJ, similar to Juno?

Launch Vehicle Performance: The launch vehicle shall deliver a minimum 6065 kg Europa Clipper spacecraft (SC) with Mars-Earth-Gravity-Assist (MEGA) trajectory characteristics as follows: C3 value of 41.69km2/sec2 and a DLA range of 30-32 degrees.

Launch Period: Europa Clipper will be launched during a 21-day launch period beginning October 10, 2024 and ending on October 30, 2024.

enter image description here

It seems like the presentation was in a Europa Clipper presentation. The trajectory seems to be as follows.

enter image description here

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    $\begingroup$ I think the answer is that the Mars flyby replaces a deep space maneuver that would otherwise be required, but I haven't found a great proof for this. $\endgroup$
    – PearsonArtPhoto
    Jan 27, 2021 at 22:08
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    $\begingroup$ The image for your simulation contains what I think is important text; Earth departure C3 = 25.5 km²/s². Am I reading it right, and is an important aspect of your question why they are requesting a higher C3 launch than seems necessary? $\endgroup$
    – uhoh
    Jan 27, 2021 at 22:12

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It seems like the biggest difference is the ability to avoid a 700 m/s deep space maneuver. That is required for a Juno style trajectory. The Mars flyby provides enough delta-v that this deep space maneuver isn't required.

In order to support the EEJ trajectory, a small booster stage would be needed to be included to provide that particular trajectory, as Europa Clipper was designed for a direct to Jupiter mission on SLS. The other option would be a Venus flyby, but that would have required some kind of a heat shield.

The information to support this all is in the question, but it took a bit to understand it.

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Supplementary answer

I was working on an answer to Are there any studies on Mars-Earth ballistic cyclers taking Mars-gravity assist into account? and I stumbled into Earth-Mars-Earth (EME) trajectories right around the current Europa Clipper timeline. I think I can add a bit to whats happening on this kind of trajectory.

Europa Clipper is taking advantage of a small niche of EME trajectories that have a very high Earth $v_{\infty}$ upon return, at the expense of a higher than typical launch C3 to Mars:

launch and arrival porkchops

(Personal work, the gaps are because the flyby at Mars has groomed out non viable dates)

I thought it was neat how this small set of EME trajectories resulted in extremely high Earth $v_{\infty}$ that enable the trip to Jupiter.

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Warning: this is a speculative answer.

I sadly would not be surprised if it were a political move to "prove" to Congress the "need" of SLS instead of relying on other launchers. Unless the Sun is in between the spacecraft and the Earth, a TCM on the way to Mars is not a big issue.

According to KSC (thanks Brendan Luke), a Falcon Heavy can launch almost 6.3 tons tons with $c_3=42 ~km^2/s^2$.

FH

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    $\begingroup$ As a post scriptum, let's note that the new policy for the Biden Admin is led by legacy aerospace corporations who seem to ignore the existence of the Falcon Heavy and Starship: twitter.com/SciGuySpace/status/1354888136376070147?s=20 . $\endgroup$
    – ChrisR
    Jan 28, 2021 at 21:48
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    $\begingroup$ elvperf.ksc.nasa.gov/Pages/Query.aspx is your friend here, It also suggests ~12.5 tons at a C3 of 10 km^2/s^2 $\endgroup$ Apr 19, 2021 at 17:10
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    $\begingroup$ @BrendanLuke15 oh this is cool, thanks! I'll fix my answer with that data $\endgroup$
    – ChrisR
    Apr 19, 2021 at 17:13

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