Xeldrak

What did you do in KSP today?

31436 posts in this topic

8 hours ago, Firemetal said:

Who needs high ISP with propellant mass like that? That is why I prefer Kerosene to Hydrogen.

The high density of kerosene lets you make the tank smaller, which improves your mass ratio (smaller tank = lighter tank).  It's still very unclear whether NASA gains anything in terms of payload to LEO by burning LH2/LO2 in their SSME derivative engine, even at their very high pressures.  And SpaceX's new Raptor runs at almost SSME pressure, but on Methane/LOX -- about the same size and weight as a Merlin, but with (IIRC) four times the thrust and higher Isp.  Liquid methane, however, is denser than liquid hydrogen, so they'll be able to get the same total impulse with about half the tank volume.

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And the Moho probe is away!

4UqLF05.jpg

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It's got a plane-change manoeuvre in 77 days and will ultimately arrive at Moho in 146 days. Between this, my probes already in place around Duna and Eve, my probe currently en route to Dres and my Jool probe waiting for its transfer window I'll soon have an unmanned presence around every body except for Eeloo.

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Today I undertook the Apollo Applications Challenge. See more here: 

 

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2 hours ago, Zeiss Ikon said:

The high density of kerosene lets you make the tank smaller, which improves your mass ratio (smaller tank = lighter tank).  It's still very unclear whether NASA gains anything in terms of payload to LEO by burning LH2/LO2 in their SSME derivative engine, even at their very high pressures.  And SpaceX's new Raptor runs at almost SSME pressure, but on Methane/LOX -- about the same size and weight as a Merlin, but with (IIRC) four times the thrust and higher Isp.  Liquid methane, however, is denser than liquid hydrogen, so they'll be able to get the same total impulse with about half the tank volume.

So you're saying that Methane is slightly better than Kerosene? I wouldn't know. The only methane fueled engines I have used are the spaceY ones.

Fire

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Well, after yesterday's medium-sized SSTO, I just had to go bigger...

E7FrNwA.jpg

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After a bizarre accident, 'Zemlya' station's orbit suddenly got shifted to 69x104. And, while fixing this, I discovered that the RSC thrusters were powerful enough to alter my orbit, raising it to 103x104. I think I'd better remove those thrusters using KAS before Bob spills his coffee on the controls again...

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Got this probe to Minmus, too bad I forgot payload 20170221214830_1.jpg

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I built my own gas giant, it took a couple billion years but in the end it was worth it.

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Sent an aggressively styled ship to a potential first contact.

XCPEOyk.jpg

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Perhaps fortunately, all the crew makes contact with is green goo.

 

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My mothership is on the way towards Otho and so I have some time to test.

As my trip to Gratian did not go as I thought it, I started to develop a SSTO for Gratian.
At first I wanted something with Aeorespikes, but the plane was too heavy. Now I have something with LVNs and it works quite well.

Here I am at the ascent.

Dt8cJ3d.jpg


And as you can see I could reach an orbit and still have quite a lot of fuel left.

2KLlHx8.jpg

In principle, it works. But during the entrance phase, I lost control twice and the plane threatened to crash. Maybe I'll put on a drogue chute so this does not happen. In general, the aircraft is not stable enough - I have to change something.
In addition, the angle of attack is too small. Maybe a few more wings. This would also help to start, as the aircraft lifts at 100m / s.

@Norcalplanner

Holy sh .... 11km / s for 3.2 Scale.

Greetings

 

Edited by astroheiko
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9 hours ago, Firemetal said:

So you're saying that Methane is slightly better than Kerosene? I wouldn't know. The only methane fueled engines I have used are the spaceY ones.

Fire

Honestly, I doubt there's much to choose between methane and kerosene.  Methane gives higher Isp, kerosene lets you use smaller, lighter tanks (methane falls between kerosene and hydrogen in both respects).  The advantage of methane for SpaceX is that sending a tank of hydrogen (no oxidizer, just H2) to Mars will let them make both methane fuel and liquid oxygen to fuel an ascent vehicle and/or return transfer -- that's ISRU in the real world, or approximately the Zubrin method of going to/from Mars.  I honestly have no idea how they'll keep hydrogen liquid for a year and a half while it gets to Mars, never mind in the Martian atmosphere after they land it and wait for the solar panels to come on line to power the conversion unit (much easier to keep the LOX and methane cold, as they're both more than 100 C warmer than LH2).

But yes, at least for hydrocarbons, the lighter the fuel (in terms of molecular weight) the more of the exhaust is (light) water vapor and the less (heavier) carbon monoxide and (heavier still) carbon dioxide -- and the lighter the average molecular weight of the exhaust, at a given chamber pressure, the higher the exhaust velocity (hence Isp).  That's part of why the NERVA engine (designed in the 1960s, but never flown, at least to date) had such high Isp: it was to use liquid hydrogen, only, at very high temperature, so had the lightest possible exhaust molecular weight and lots of energy in that exhaust.

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