Skylon v SpaceX: A community challenge

[sevenperforce]

37 minutes ago, michal.don said:

Hello again,

I completed the three missions in a SSTO.I present: the PseudoSkylon

The dry mass in 28,889 tons and it runs on four RAPIERs and one Terrier as an OMS engine.

Here are the missions:

http://imgur.com/a/heEmp

http://imgur.com/a/HAizr

http://imgur.com/a/ZP7Uy

 I'll enjoy being the best entry for a while, until the spaceplane guys come

Michal.don

Simply gorgeous! A really, really impressive job.

[qzgy]

Currently working on tsto entry. Boostback is hard...

[sevenperforce]

On 7/29/2017 at 9:13 PM, qzgy said:

Currently working on tsto entry. Boostback is hard...

Yes, it is! I've tried it quite a few times now. 

[Sensi]

OP, may I ask you why Sabre engines aren't allowed? After all, they were built especially for Skylon...

And as far as I know, although some hydrogen will be used to cool helium in the closed-cycle precooler, it will still be burned in the engines' combustors after cooling the helium loop. That means that 100% of the hydrogen will be used as fuel. So, why do you limit the LF quantity to 50%?

[sevenperforce]

14 minutes ago, Sensi said:

OP, may I ask you why Sabre engines aren't allowed? After all, they were built especially for Skylon...

And as far as I know, although some hydrogen will be used to cool helium in the closed-cycle precooler, it will still be burned in the engines' combustors after cooling the helium loop. That means that 100% of the hydrogen will be used as fuel. So, why do you limit the LF quantity to 50%?

Sabre engines (well, the RAPIERS) are absolutely allowed. That's what is required for the spaceplane SSTO version.

The bypass hydrogen will be burned in bypass ramjets, not in the main combustion chamber (it requires more hydrogen to precool than it can use). But the reason for LF limitation is that real-life hydrogen is VERY lightweight and not dense at all. Tankage ratio on stock tanks is way too good for hydrogen (though worse than most bipropellant rockets).

[Sensi]

IG, the Rapier engine is not equal to the Sabre engine (3200 Isp vs 4800 Isp). IRL, the Rapier engine is a 16-cylinder H pattern air-cooled aero engine built in 1929

As for the fuel, fair enough. Your challenge, your rules.

[michal.don]

8 minutes ago, Sensi said:

IG, the Rapier engine is not equal to the Sabre engine (3200 Isp vs 4800 Isp)

That is true, but on the other hand, the orbital velocity on Kerbin is around 2300 m/s compared to 7800-ish m/s in LEO. SSTO in the real world is really difficult and if it is ever succesfully designed, will get to orbit with very tight margins. The limitation of 50% fuel makes it difficult, but not impossible, so I think it approximates the "real" SSTOs quite well.

Michal.don