Hacker News Reader

Comment by wongarsu | Hacker News Reader

If you launch to the west this might be viable. The government wouldn't be particular thrilled about test flights over land (or any flight over land), but for a test flight you would want something longer than a jump across the continent anyway.

View on HN

Rockets rarely launch at a retrograde (western) orbit because you have to overcome the earth’s rotation to reach orbital velocity, rather than the speed boost you get from launching with the earth’s rotation. IIRC, satellites launching from Vandenberg AFB in California take a polar orbit.

Even if they went all the way up to the ISS's orbit (which would be useless both because it's a test flight and because they would be going the wrong direction), the difference between going in a western or eastern orbit is a ~10% difference in delta-v requirements. Normally that's an enormous difference, but if you can just decrease the size of the test payload at will it shouldn't matter much beyond spending a few thousand dollars more on fuel.

It's not the height that counts, it's the sideways speed. Getting to 250 miles above sea level is relatively easy. Getting to 5 miles a second it far harder.

But if you're not aiming for orbital velocity the earth's rotational speed doesn't make any difference -- the relative speed of start and end points are the same. It doesn't take more fuel to travel west than east because of the rotation of the earth (jet stream sure, but if rockets are affected by the jet stream there's something seriously wrong)

Disclaimer: my entire picture of orbital dynamics comes from KSP

Check your orbital velocity at the surface. It's not 0. The direction you head does matter.

OTOH if they're just trying to get from California to Florida they don't need full orbital velocity.

Reply on news.ycombinator.com