# Why is NASA proposing an EMEJ (MEGA) trajectory for Europa Clipper instead of EEJ?

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.

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

• 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. – PearsonArtPhoto Jan 27 at 22:08
• 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? – uhoh Jan 27 at 22:12

## 2 Answers

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.

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 $$c_3=42 ~km^2/s^2$$.

• 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 . – ChrisR Jan 28 at 21:48
• 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 – BrendanLuke15 Apr 19 at 17:10
• @BrendanLuke15 oh this is cool, thanks! I'll fix my answer with that data – ChrisR Apr 19 at 17:13