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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.

uhoh
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  • From winchell chung's twitterhttps://twitter.com/nyrath/status/1025399615435300864?s=20:

    I can't thrive on ion drive.

    I need that rocket to burn.

    Kick the ass, give it the gas.

    I've got that need... for ISP

    Solar sail is an epic fail.

    I need that rocket to burn.

    Full on thrust is what I lust.

    I've got that need... for ISP

    Cn you say Constant acceleration?

     – ikrase Oct 16 '20 at 11:36

1 Answers1

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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.

  • Dawn- 22.89 km/s
  • PSP- ~17.2 km/s
  • New Horizons- 17.61 km/s
  • Cassini- 15.69 km/s
  • Juno- <14.5 km/s

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.

asdfex
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PearsonArtPhoto
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  • What numbers do you get for Cassini and Juno, the "flying fuel tanks" I've linked to in the question? Cassini got all the way to low Saturn orbit before entering the atmosphere. While it used Titan for some perturbation, it did use a whole heck of a lot of propellant. Can you confirm quantitatively that it doesn't belong in the top three? Googling "delta-v to Saturn" sends us back to Space SE https://space.stackexchange.com/q/41718/12102 but there should be specs. And Cassini did literally hundreds of propulsive maneuvers while there, and climbed to 64 degrees inclination before the end. – uhoh Oct 15 '20 at 19:51
  • I'll do some number crunching, but I doubt it is any higher. Cassini in particular took a very circuitous route to Saturn to save fuel, so... – PearsonArtPhoto Oct 15 '20 at 19:56
  • which it needed when it got there, so... Why would Cassini need to reach 64 degrees inclination before “threading the needle”? and Unravelling Cassini's “ball of yarn” orbit around Saturn, tabulation of propulsive maneuvers? and Is Cassini running out of fuel? and Is Cassini's 183rd burn; some kind of engine record? It wasn't an accident that I linked to the flying fuel tanks in the question. – uhoh Oct 15 '20 at 19:57
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    I chose the missions that I did because I knew that ion propulsion is VASTLY better than chemical propulsion. I'm not aware of any staged missions beyond the initial rockets besides lunar missions, and I know the energy use to get from there is quite low. Cassini achieved the pretty incredible journey through Saturn almost entirely because of gravitational flybys of Titan. I saw an estimate that it was worth about 80 km/s, making that the likely king of gravitational assists. – PearsonArtPhoto Oct 15 '20 at 20:06
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    Also, I did include a source for both of Cassini's relevant numbers, so... – PearsonArtPhoto Oct 15 '20 at 20:07
  • I'll go back to neutral for now, will check in tomorrow, but are you sure these are all 100% propulsive? Didn't for example New Horizons get a gravitational bump from Jupiter? Didn't Dawn get one from Mars? You can't just use C3 if there are assists. – uhoh Oct 15 '20 at 20:16
  • Solar sails are "obviously" cheating, but how well does your ion drive work when you turn off the sun? – SE - stop firing the good guys Oct 15 '20 at 20:59
  • @SE-stopfiringthegoodguys If your civilization can turn off a sun, I suspect the delta-v available to your spacecraft is a bit better than turn-of-the-21st-century ion drives can pull off... – notovny Oct 15 '20 at 21:48
  • I'm surprised that Dawn has that little dV - what's it's mass ratio? – ikrase Oct 16 '20 at 02:51
  • Looks like about 1.54, well below the optimum. I'm guessing that with gaseous propellant, the tanks are unavoidably going to be heavy – ikrase Oct 16 '20 at 02:57
  • -1 because by simply using C3 one also includes gravitational assists, which are not propulsive. Can you list the propulsive delta-v for each craft to make a fair comparison? Your New Horizon links for example contains "post-launch delta-V requirements were over 11 km/sec " but does no say how much is from the February 2009 Mars gravity assist. Likewise New Horizons did a gravitational assist at Jupiter. The question specifically asks for propulsive delta-v. – uhoh Oct 16 '20 at 03:39
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    C3 does not include gravity assists... How on Earth will ULA, which is where I sourced most of the numbers, know the location lifetime gravitational assists of a spacecraft? At best it includes an optimal time to burn from Earth, but that hardly counts... I did have a slight error converting from C3 to peak velocity, and have updated the answer accordingly. – PearsonArtPhoto Oct 16 '20 at 05:00
  • From this answerr I have $$v^2=C_3+2\frac{GM}{r}$$ I can't tell how you are using C3 exactly and no idea where "$\sqrt{{V_E}^2 \cdot C_3}$, where ${V_E}^2 = 11.19 km/s$" comes from. Can you show your math clearly so it will be clear how you are getting these numbers and cite a specific resource where the equations can be verified? C3 has units of velocity squared so your equation's units don't work. You can see how I show the math in that linked answer so that anyone can check and verify it. Here we have to take your word for it; right now I don't – uhoh Oct 16 '20 at 11:55
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    Typed the wrong thing, but I did the right thing in my calculations. Basically VE is the escape velocity of Earth, and the rest is converting the right portion of your equation to terms of escape velocity and taking the square root. – PearsonArtPhoto Oct 16 '20 at 11:58
  • As far as assists are concerned, I think that you are using "The injection C3"? – uhoh Oct 16 '20 at 11:58
  • If you show your math clearly it can be checked and we don't have to discuss. Right now I can not judge the veracity of this answer because we just have to take your word for it. – uhoh Oct 16 '20 at 11:59
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    I am totally ignoring gravitational assists, as you wanted just propulsive maneuvers. The only assist of any kind is the oberth effect, but... – PearsonArtPhoto Oct 16 '20 at 11:59
  • Dawn link: Ion Propulsion enabled the Dawn mission, where the post-launch delta-V requirements were over 11 km/sec "post-launch requirement" doesn't distinguish clearly between ion propulsion and the gravitational assist as it passed within 550 km of Mars. I understand that you don't intend to include it, but it's not clear from those few words on a PowerPoint slide that that's only propulsive post-launch and not total post-launch. Can you find a better orbital-mechanical source than some slides by a thermal engineer? – uhoh Oct 17 '20 at 10:38
  • If you can link to this answer which provides a source for that equation (which I can now safely believe because it is thoroughly explained there) and mention that your $C_3$ values are geocentric and not heliocentric, that would be great and I can remove the down vote. – uhoh Oct 18 '20 at 12:55