Fun With Numbers
I get off on these tangents sometimes...
Things started innocently enough. I was just thinking about the potential for using a 2-stage Zenit Sea Launch vehicle for sending propellants or people into LEO (more on that in a later post). Then I notice...hey wait a second...Zenit uses the RD-171 engine. Isn't that the 2-axis gimballed version of the engine from which the Atlas V's RD-180 was derived? Wasn't the plan for Atlas V Evolution Phase II supposed to be going to a bigger first stage with two RD-180s? So, I pull up some numbers I had found for the propellant and dry masses would be for the Atlas V Phase II core stage, and compared them. Drats! Too little propellants. More than the current Atlas V core by about 15%, but less than the Atlas V Phase II core by a substantial margin.
Then I scratch my head...this thing has something like 1.6Mlbf liftoff thrust, but that small of a first stage? How big is the second stage on this bad boy?
Oh. 200klb...That's kinda big, isn't it.
Hey...I wonder...
What would happen if you tricked this bad boy out with a LOX/LH2 WBC stage? The 3.5x sized WBC with 4-6 RL10s is a bit lighter than the fully loaded Zenit-2 Stage 2. So I run the numbers...
58,000lbs to a 51.6 degree, 200km circular orbit. Hot dang, that's better than the Shaft. Heck that's more than Delta-IVH! You know, with Boeing and Lockheed getting all buddy-buddy with the ULA, maybe they should get together...
Not that there's a chance in heck that this would happen. Buying a good rocket stage from someone else instead of blowing billions on a mediocre one made here in the USA would be unpatriotic. Heck, it'd even be capitalist! We can't have that, can we?
Just sayin...
I get off on these tangents don't ya know.
Things started innocently enough. I was just thinking about the potential for using a 2-stage Zenit Sea Launch vehicle for sending propellants or people into LEO (more on that in a later post). Then I notice...hey wait a second...Zenit uses the RD-171 engine. Isn't that the 2-axis gimballed version of the engine from which the Atlas V's RD-180 was derived? Wasn't the plan for Atlas V Evolution Phase II supposed to be going to a bigger first stage with two RD-180s? So, I pull up some numbers I had found for the propellant and dry masses would be for the Atlas V Phase II core stage, and compared them. Drats! Too little propellants. More than the current Atlas V core by about 15%, but less than the Atlas V Phase II core by a substantial margin.
Then I scratch my head...this thing has something like 1.6Mlbf liftoff thrust, but that small of a first stage? How big is the second stage on this bad boy?
Oh. 200klb...That's kinda big, isn't it.
Hey...I wonder...
What would happen if you tricked this bad boy out with a LOX/LH2 WBC stage? The 3.5x sized WBC with 4-6 RL10s is a bit lighter than the fully loaded Zenit-2 Stage 2. So I run the numbers...
58,000lbs to a 51.6 degree, 200km circular orbit. Hot dang, that's better than the Shaft. Heck that's more than Delta-IVH! You know, with Boeing and Lockheed getting all buddy-buddy with the ULA, maybe they should get together...
Not that there's a chance in heck that this would happen. Buying a good rocket stage from someone else instead of blowing billions on a mediocre one made here in the USA would be unpatriotic. Heck, it'd even be capitalist! We can't have that, can we?
Just sayin...
I get off on these tangents don't ya know.
Labels: Launch Vehicles, Space Development
posted by Jon Goff at 7:42 PM
4 Comments:
Zenit is an excellent booster with good value for the money. So good in fact that Boeing withdrew Delta from the satellite launch business to avoid the need to compete on price.
Yeah, Sea Launch is definitely a lot more commercially useful than the Delta IV currently is. In its two-stage version, it can put almost 50% more into LEO than a single-stick Atlas V 401. The only bad thing about it is that it doesn't have as good of a record as the Atlas V.
I wonder though if Boeing might not try following Lockheed's lead and human-rate the Zenit.
~Jon
Funny to compare the Stick with Zenit. After all, they were both designed as strapons for the shuttles.
Which brings me to another point - isn't Zenit man-rated already given that it was developed for a manned system?
Jv,
Just out of curiousity, I decided to compare the SRB to the Zenit-1 Stage, since as you say, both were designed as strapon boosters.
The Zenit-1 produces about 1.6Mlbf, and weighs about 781klb, the SRB produces about 2.6Mlbf and weighs about 1300klb. Roughly comparable T/W ratios for the stages. However the Zenit-1 has a Mass Ratio of about 12, and the SRB only has an MR of about 6. Also the Zenit-1 has a sl Isp of 311s, while the SRB has about a 237s sl Isp.
What this basically means is that the SRB could produce about 4.4km/s of Delta-V by itself, while the Zenit-1 is probably almost an SSTO stage...
Yar!
As for being man-rated...yeah, it's about as manrated as the SRB...but unfortunately that doesn't mean very much. The Zenit-1 stage has about a demonstrated ~97% reliability, while the SRB has a demonstrated ~99% reliability. But I'm willing to bet that escaping a failing Zenit-1 stage is a lot safer than escaping a failing SRB...
All in all, it's definitely an interesting numbers game.
~Jon
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