LauncherOne: Virgin Galactic's other project | Hacker News Reader

LauncherOne: Virgin Galactic's other project

bbc.co.uk

I've always been unsure on the British governments current policy to avoid funding any space projects.

On one hand they're forcing Virgin Galactic to become financially independent and not to rely on government handouts and be ultimately indebted for their existence.

Yet on the other hand, it appears as though the government isn't invested in their success and that they're happy to let NASA and the ESA deal with everything space related. Yet we all know, the first successful satellite launch by Virgin will be praised to no end by the British government as a 'made in Britain' triumph.

This sounds like someone hoping to get a gov grant but obfuscates the real issue: once detached from the mother ship the rocket still needs to accelerate from around 4-500 mph to 17k mph to reach orbit.

Indeed the acceleration must occur, but starting at 50k feet substantially reduces the amount of air the rocket has to push out of its way.

This not only makes acceleration easier, it also dramatically reduces the dynamic pressure on the vehicle at max Q, allowing for a reduction in the mass of the vehicle (making acceleration easier still).

Air launch makes a few things easier. You save a little bit on the inefficiency of fighting gravity for those first few seconds getting off the ground, you save a lot more by easing the design envelope of your rocket nozzle.

It's difficult to make a rocket nozzle that works efficiently at the range of pressures from sea level to vacuum, at 50,000 ft atmospheric pressure is nearly 0.1 atm. Because of the exponential nature of the rocket equation even a slight increase in engine Isp can translate to a significant increase in payload (or decrease in vehicle size) or even cross the line of capability. For example, LOX/Kerosene engines tend to top out at a sea level Isp of around 309 seconds, though upper stage LOX/Kerosene engines have been built with vacuum Isps of 353 seconds. This translates to 17:1 and 12:1 mass ratios, which easily makes the difference between feasible and infeasible rockets (17:1 is at the edge of rocket building techniques, 12:1 well within it).

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