# Can jet engines be used to launch a rocket?

Following up on my previous question Can a VASIMR Plasma engine be used to launch a rocket?, I was told that VASIMR plasma thrusters are inefficient in an atmosphere. I then had the idea of using jet thrusters as in the ones that are used on airliners.

It may be wise to look at the previous question for reference.

The spacecraft weighs close to 700Tons and is 300m long.

Also a part 2 to the question:

Jet engines on airliners use fuel I assume, is it possible for pure electric thrusters to move the craft in a harrier style takeoff?

• Read my previous question – Tim Li Dec 3 '19 at 21:16
• Yes. The LLRV which was the LM simulator used a jet engine positioned perpendicular to the ground. The LLRV – Star Man Dec 3 '19 at 21:26
• @StarMan it wasn't electric though. Note: I am in no way endorsing this concept, it appears to be an attempt to maximize inefficiency. – Organic Marble Dec 3 '19 at 21:31
• Many drones use ducted electric fans in a quadcopter arrangement. They're not going to get you anywhere close to orbit though. – Christopher James Huff Dec 3 '19 at 22:45
• Are you asking about jet engines (i.e. the kerosene-burning devices that power aircraft) , electric-powered fans or something else? – Hobbes Dec 4 '19 at 7:34

The commercial CF6-80C2 engine has a mass of about 5T and a thrust of about 300kN, including intake and nozzle thrust at takeoff. As heavy commercial engines go, it’s about the best for this application.

That thrust can provide 1g upward acceleration to about 15T total mass. Subtracting its mass and allowing a bit for fuel (at full thrust it burns 3kg a second, so it’s not so bad compared to a rocket), and maybe a bit for structure, you could lift maybe 7T with one.

To lift 700T, you’d need about 100 of these. Just enough room for those around the edges!

They’re pretty cheap, about \$12M each, so you’re looking at \$1.2B for your first-stage power. Maybe you could get a quantity discount?

Each engine has roughly 50MW shaft power. I don’t know whether an electric motor would be heavier or lighter, but you’d also need to account for a 5GW power source. Perhaps four or five Mr Fusions would do.

So as a school drawing, this is sort-of within reach.

• @hobbes good catch! Thank you. Fixed. – Bob Jacobsen Dec 4 '19 at 13:56
• Thanks for that. Is there any way the the fuel supply or fuel consumption could be more efficient? Is it possible for it to consume solid fuel? – Tim Li Dec 4 '19 at 20:24
• @TimLi Jet engines already approach their theoretical maximum. And solid fuel would be less efficient, not more. – Hobbes Dec 5 '19 at 7:57