Tuesday, March 8, 2011

Who Needs a Heavy Lift Launch Vehicle?

Space agencies and corporations alike have expressed interest in developing a heavy lift launch vehicle (HLLV). Though the terminology varies, I am referring explicitly to launch vehicles that can lift more than 50,000 kilograms (kg) to low Earth orbit. These are sometimes referred to as "super heavy lift" launch systems, probably because they would be among the most powerful rockets ever flown. As far as I am aware, only three launch vehicles ever lifted more than 50,000 kg to space: the Saturn V, the Space Shuttle, and the Soviet Energia rocket. The Saturn V could lift 118,000 kg, while the Space Shuttle and Energia could lift about 100,000 kg including the mass of their reusable orbiters.

Ares V rocket concept
The Ares V rocket was to lift more mass
than any other launch vehicle in history
The problem with HLLVs is that they're not an economical way to lift mass into orbit. These enormous launch vehicles have a great deal of structure that does not end up in orbit because they have to be made of strong, heavy materials. Smaller rockets can be made of lighter materials because they do not need to support all that weight—both payload and fuel—above them. An HLLV will also typically require much more sophisticated engines to generate the thrust necessary to reach space. This added complexity can quickly introduce new costs as developers seek to match the reliability of smaller, more manageable rockets.

It seems the only redeeming aspect of HLLVs is the capability to launch huge payloads in one piece. Even if it were more expensive per kilogram to use an HLLV than a smaller alternative, there may be some spacecraft that cannot be split into two launches. However, I cannot imagine many payloads that fit this description. Unpressurized space modules can often be folded up and deployed once in space, while pressurized modules can fit inside smaller launch vehicles if they are made to be inflatable—like the modules under development by the company Bigelow Aerospace. If these separate modules could autonomously rendezvous and dock with each other after reaching orbit, who would pay extra to use a heavy lift launch vehicle?

2 comments:

  1. The shuttle at 24k kg payload is at the lower end of heavy lift. You can't count the orbiter as payload. It's not super heavy.

    How economical a vehicle is depends on a number of factors not easily summarized.

    I agree that HLLVs aren't currently required. We have plenty of capability (with more coming) for current needs. If we spent $300m to put a fully refuelable general purpose vehicle (GPV) in orbit using existing launch systems and components (already tested in orbit) we could start to get operation experience and establish a market for RP-1/LOX to orbit. Anybody with $300m could get on the phone and put the order in today.

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  2. I don't mean to imply the shuttle stack or Energia rocket can lift 100k kg of useful payload into to orbit. Just that those rockets did lift something that heavy into space--the orbiters themselves.

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