Descartes Propulsion?

[EnDSchultz]

Hey all,

Just a completely random and inconsequential question. I'm very fascinated with the Descartes line of vessels and was curious about its method of propulsion. The manual only gives a few details about its modular design and some history regarding the construction process and its history of service but never really got into any details of the engineering behind it. Has the author of this great vessel put much thought into such things?

Edit: Also, on the subject of propulsion, what sort of dV does everyone get with it? I just used up 2/3 of its fuel on a 7.7km/s dV out of Mars. Isn't that little low for something advertised as an interplanetary vessel?

 

[Mindblast]

Yes the Descartes has very low dry mass and huge amounts of fuel on board. So it feels like low overall dV after the first burn but actually it has quite ok dV. I just looked at the numbers and calculated overall dV as 26223m/s. The ISP is 7500m/s so probably some kind of nuclear engine. Probably the main engines have a bit high thrust too as they could produce up to 8G accelleration with an almost empty fueltank.

 

[Sky Captain]

Yes the Descartes has very low dry mass and huge amounts of fuel on board. So it feels like low overall dV after the first burn but actually it has quite ok dV. I just looked at the numbers and calculated overall dV as 26223m/s. The ISP is 7500m/s so probably some kind of nuclear engine.

A 7500 m/s exhaust velocity is a bit low for nuclear rocket. IIRC the NERVA prototypes achieved something like 9000 m/s and that was 30 years ago. I suppose a futuristic exploration vessel like Descartes should have at least a gas core nuclear engine with ISP of 30000 - 40000 m/s.

 

[the.punk]

A 7500 m/s exhaust velocity is a bit low for nuclear rocket. IIRC the NERVA prototypes achieved something like 9000 m/s and that was 30 years ago. I suppose a futuristic exploration vessel like Descartes should have at least a gas core nuclear engine with ISP of 30000 - 40000 m/s.

Yes gas core reactor or maybe fusion propulsion. Or something like a VASIMR. They have also high ISP.

 

[EnDSchultz]

Yes the Descartes has very low dry mass and huge amounts of fuel on board. So it feels like low overall dV after the first burn but actually it has quite ok dV. I just looked at the numbers and calculated overall dV as 26223m/s. The ISP is 7500m/s so probably some kind of nuclear engine. Probably the main engines have a bit high thrust too as they could produce up to 8G accelleration with an almost empty fueltank.

That dV estimate seems a bit too high. My trip from Mars to Mercury almost emptied my tanks (3% remaining now), and according to IMFD, the total dV was only about 15.0k total for escape and insertion; add onto that no more than 5.0k for plane changes and corrections and it seems something's wrong...would it be reasonable to go into the .ini files for the Descartes vessels and increase the ISP to something more like 10,000?

 

[Brycesv1]

descartes is a dll vessel i think... so the answer to your question would be no

 

[EnDSchultz]

Well there is an .ini file for each of the Descartes vessels, 01-05, and they all have ISP variables in them...what would be the harm in altering that?

 

[Brycesv1]

the dll takes priority over other files so no matter what you change it to, the dll will still force the isp to whatever it wants

 

[Linguofreak]

A 7500 m/s exhaust velocity is a bit low for nuclear rocket. IIRC the NERVA prototypes achieved something like 9000 m/s and that was 30 years ago. I suppose a futuristic exploration vessel like Descartes should have at least a gas core nuclear engine with ISP of 30000 - 40000 m/s.

Nerva had 8000, and keep in mind that not much real work has been done on such engines in the past 30 years. I've heard solid core NTR's discussed up to 12,000 m/s, and liquid cores up to 16,000.

 

[Ark]

the dll takes priority over other files so no matter what you change it to, the dll will still force the isp to whatever it wants

The Total Immersion .dll takes it's values from the #5's SC3 config file. Changes made to that file are carried over to the TI version in-game.

 

[Mindblast]

That dV estimate seems a bit too high. My trip from Mars to Mercury almost emptied my tanks (3% remaining now), and according to IMFD, the total dV was only about 15.0k total for escape and insertion; add onto that no more than 5.0k for plane changes and corrections and it seems something's wrong...would it be reasonable to go into the .ini files for the Descartes vessels and increase the ISP to something more like 10,000?

That seems about right, you should get another 5353 m/s out of those 3% fuel left. Thats what i meant.. the Descartes has an empty weight of 125tons with 4000tons of propellant. so if you are down to 3% of your 4000 tons its still 120tons propellant left.. almost as much as the empty weight of the ship.. and with 9.5MN of thrust from the main thrusters you should get like 4g acceleration.

Btw. the engines are ridiculously overpowered.. 9.5MN thrust at 7500m/s ISP.. thats 35.6 GJ/s (GW) of kinetic energy of the exhaust. That'd be a pretty big nuclear reactor..