An SSTO as "God and Robert Heinlein intended".

[orbitingpluto]

Pure dV derived from rocket equation is not enough. You have to acount for gravity losses, which are determined mostly by thrust/weight ratio in initial phases of flight.

Silverbird rocket calculator says that Titan 1st stage with single LR-87-5 can't achieve orbit on it's own. Adding second engine to the stage gives me astonishing payload of 28kg! And that's for straight eastward launch on equator.

My thrust values are about one-half of the actual, thanks to some Wikipedian who thoughtfully decided to list the specs of the LR-87-5 as if there was only one combustion chamber. I did go ahead and post it without sanity checking it first, so I'm glad you caught my error.

Anyway, I do know the Titan 2 first stage is marginal on usefulness as a SSTO(in my opinion at the very least), and the idea of making it a space plane doesn't make sense to me- but it did seem a passable reason to hand out resources so someone so they can use the rocket equation to explore how rocketry works. My estimate of ~9000 m/s does include margin for gravity losses and drag, but I do realize I was making things a bit too simple. :shrug:

 

[Urwumpe]

My estimate of ~9000 m/s does include margin for gravity losses and drag, but I do realize I was making things a bit too simple. :shrug:

The conservative estimate is 9200 m/s.

You can lower this - but practically, this means stuff like accelerating with 12 g or having a white glowing nose.

 

[RGClark]

Pure dV derived from rocket equation is not enough. You have to acount for gravity losses, which are determined mostly by thrust/weight ratio in initial phases of flight.

Silverbird rocket calculator says that Titan 1st stage with single LR-87-5 can't achieve orbit on it's own. Adding second engine to the stage gives me astonishing payload of 28kg! And that's for straight eastward launch on equator.

That might be due to the various versions of the Titan II that were made. I noticed that dry mass value you used was higher than the cited Wikipedia value. Wikipedia is sometimes inaccurate but here's another more reliable source that gives a lower value for the dry mass of the Titan 2G version of the titan

http://www.braeunig.us/space/specs/titan.htm

Bob Clark

 

[Urwumpe]

That might be due to the various versions of the Titan II that were made. I noticed that dry mass value you used was higher than the cited Wikipedia value. Wikipedia is sometimes inaccurate but here's another more reliable source that gives a lower value for the dry mass of the Titan 2G version of the titan

http://www.braeunig.us/space/specs/titan.htm

Bob Clark

Dry mass or empty mass is not burn-out mass.

 

[RGClark]

Pure dV derived from rocket equation is not enough. You have to acount for gravity losses, which are determined mostly by thrust/weight ratio in initial phases of flight.

Silverbird rocket calculator says that Titan 1st stage with single LR-87-5 can't achieve orbit on it's own. Adding second engine to the stage gives me astonishing payload of 28kg! And that's for straight eastward launch on equator.

The Wikipedia page on the Titan II is confusing but actually it did use two LR-87's on the first stage. So your entry for the thrust is actually the correct one for the two engines used. I already mentioned at least one version of the Titan II only had a dry mass for the first stage in the 4,300 kg range.

There is also a quirk of the calculator you need to be aware of. The option "Restartable Upper Stage", you would think wouldn't matter if it is only a single stage. But I think it takes the last stage firing as the upper stage, so keeps some propellant in reserve even for a SSTO. In any case it results in a significant loss in the payload if you leave the "Yes" option checked here.

Bob Clark

 

[TheMineGamer32]

Thanks, orbitingpluto! I work with it in Christmas, because I'm studying and working on the Pegasus (I have the Stargazer, Pegasus, Iris, Ibex and Aim payloads working properly, but Aim's solar panels don't work):facepalm: And I have to finish the repairing of the Minotaur I add-on.

 

[RGClark]

Another highly weight optimized stage was the S-II second stage on the Saturn V. According to this Wikipedia page it was even better optimized than the S-IVB stage :

Saturn V.
S-II second stage.
http://en.wikipedia.org/wiki/Saturn_V#S-II_second_stage

The 5 J-2 engines used had a mass of 1,580 kg each, for a total mass of 7,900 kg. You'll need 3 of the SSME's operating at 109% thrust to lift the mass. So the 7,900 kg mass of the engines is replaced with 9,300 kg. And the 36,000 kg S-II dry mass is raised to 37,400 kg and the gross mass is raised to 481,400 kg.
Now using Gary Hudson's 425s trajectory averaged Isp for the SSME engines, and the 9,200 m/s required delta-V to orbit. We get a 17,000 kg payload:

425*9.8ln((481400 + 17000)/(37400 + 17000)) = 9,225 m/s

However, again we can get 10% greater total mass to orbit by propellant densification. This brings the payload to 22,440 kg. Also perhaps 10% off the structural mass can be saved by using aluminum-lithium alloy. And an additional 10% mass can be saved by the new weight saving methods. These weight savings can go to extra payload to bring the payload mass up to 28,000 kg. Note this is sufficient now to carry the Orion spacecraft as a SSTO.

More accurate calculation for a reusable S-II as an SSTO:

A Vertical Landing SSTO - a "Space Shuttle" NASA Missed.
http://exoscientist.blogspot.com/2015/05/a-vertical-landing-ssto-space-shuttle.html

Bob Clark

 

[MaverickSawyer]

The Wikipedia page on the Titan II is confusing but actually it did use two LR-87's on the first stage. So your entry for the thrust is actually the correct one for the two engines used. I already mentioned at least one version of the Titan II only had a dry mass for the first stage in the 4,300 kg range.

Correct. The LR-87 family was never used in a single engine installation, so most people reasonably assume that it's a two-chamber engine and give the specs for it in the Titan configuration. This tends to include the mass of the gimbals, actuators, structural frames, and the shared turbopumps that were used in this format.