What's the most efficient engine

[The_space_travveler]

I'm doing a mission with a huge delta V requirement, and I wondered, which would be better, a nuclear engine, or an ion engine?

[GluttonyReaper]

Short answer - the ion engine. It's got a higher ISP and it's lighter, so if you only care about dV, that's what you should go with.

However, there are some caveats. First, the ion engine has a tibblingly low thrust, so it's (almost) useless for landers... and can result in some painfully long transfer burns. Second, it needs a supply of electric charge - if you're not going too far away from the Sun, you can use solar panels, but regardless you're going to have to carry some extra weight. This can be somewhat mitigated by throttling down, but then you end up with an even lower thrust. Thirdly, don't necessarily rule out chemical engines straight away - if your payload is small, a tiny engine and a big tank can go a long way, especially with the benefit of staging.

[The_space_travveler]

Thanks for the help! i ended up using a small engine on a small probe. : )

[Duke MelTdoWn]

Small is the way to go! "Simplify, then add lightness" - Colin Chapman, allegedly.

I like to do manned missions and love the Nerva. The main benefits I see:

- Good ISP
- Runs on liquid fuel. LF is much lighter than LF+OX, making the fully tanked craft lighter.
- Low thrust but enough for landing on most planets
- LF can be produced with ISRU while Xenon can not

You might also consider a combination like Nerva for interplanetary transfer and small lander with single terrier for landing.

[DareMightyThingsJPL]

5 hours ago, Duke MelTdoWn said:

Small is the way to go! "Simplify, then add lightness" - Colin Chapman, allegedly.

I like to do manned missions and love the Nerva. The main benefits I see:

- Good ISP
- Runs on liquid fuel. LF is much lighter than LF+OX, making the fully tanked craft lighter.
- Low thrust but enough for landing on most planets
- LF can be produced with ISRU while Xenon can not

You might also consider a combination like Nerva for interplanetary transfer and small lander with single terrier for landing.

There are downsides to the Nerva, too:

- High mass means that it cuts into your payload mass, and with low amounts of fuel, it's high Isp is often offset by this.

- It's prone to overheating when operating close to the sun: not good for solar oberth boosting.

- It has a large vertical footprint, complicating lander design.