Space Exploration Asked on January 20, 2021
How fast is fuel escaping a rocket for it to reach the escape velocity 11 km/s? was an active and well-received discussion! It’s always exciting when we first realize that a rocket can go much faster than its exhaust velocity.
Chemical exhaust is in the 2 to 4 km/sec ballpark but deep space probes can get maybe five (or ten?) times that speed propulsively thanks to staging.
Some of the deeper, faster probes have been flying fuel tanks so they can go far, then slow down enough to get captured, then do more maneuvering for years.
Question: Not counting gravity assists and only counting propulsive maneuvers, what spacecraft has had the greatest total propulsive delta-v?
I don’t know if answering will be easier if you include all delta-v staring from the launch pad, or only delta-v once deployed from a rocket. The problem is that there are solid boosters and it can be argued either way if they count as a stage or as payload. So if I had to offer guidance I’d say be inclusive. Start from either the ground, or better yet from LEO, since LEO also includes launching from the shuttle or the ISS.
Almost certainly the vehicle with the most Delta-v post-booster separation was the Dawn spacecraft, with an incredible 11 km/s! Put another way, that is the same amount as the rocket that launched it roughly. This is because of the unique nature of an ion drive, being vastly more efficient than chemical rockets. If it were a chemical rocket, it would have to be a staged chemical rocket, and I really haven't seen anything about those, except for lunar return missions. The other ones have been atmospheric landers, but they really don't have much rocket power to land.
Any contender will either be using an ion drive for a long duration mission, or else be put on a very energetic orbit from the Earth, if we count that. As Dawn had the largest ion engine tanks ever developed, that is almost certainly the winner there.
If one includes the rocket energy, let's look at C3, and then add in any delta-v beyond that. The two most energetic missions in terms of C3 were Parker Solar Probe (154 km²/s²) and New Horizons (170 km²/s²). Dawn's C3 was 11.4 km²/s². New Horizons had a post-launch delta-v of 290 m/s, and Parker Solar Probe was small, although I can't find the exact number, but it was small. I'm just going to assume the same 300 m/s.
Other contenders include Cassini, with a C3 of 16.6 km²/s² and a delta-v of 2.4 km/s, and Juno with a C3 of 31.1 km²/s². I can't find the Juno delta-v, but it should be less than 3 km/s. It is worth noting that Cassini was able to achieve dramatic orbital changes by flying by Titan, on the order of 80 km/s.
Taking all of this in to account, the delta-v of each space craft defined as spacecraft only delta-v + $sqrt{{v_E}^2 + C_3}$, where ${v_E} = 11.19 ~rm{km/s}$, the escape velocity from Earth. The latter part converts the $C_3$ to the effective delta-v, when taking in to account losses from atmospheric drag, gravity drag, ineffective trajectories, etc. This seems to be the fairest way to calculate the effective delta-v. Taking all of this in to account, the following is the delta-v.
Even with that metric, it seems like Dawn is a pretty clear winner. That high delta-v allowed it to orbit two different large asteroids.
Of some note is the Europa Clipper mission, which if launched on SLS will have a C3 of ~80 km²/s² and a delta-v of only around 2 km/s. A Europa lander would be required to have much more delta-v of 4.3 km/s. Still, that only adds up to around 16.5 km/s to 18.8 km/s, Dawn is still the clear winner.
Answered by PearsonArtPhoto on January 20, 2021
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