Comment by benjaminl | Hacker News Reader

Comment by benjaminl | Hacker News Reader

This graphic aptly shows the differences in complexity between the two flight plans, but it doesn't show the biggest difference between the two rockets. When the Falcon 9, enters space at the height of 100 km, it is traveling at 5000 km/h with 125 metric tons of payload[0]. Blue Origin's New Shepard, the best I can tell was traveling at ~0 km/h at that height, as it reached apogee at the height of 100.5 km and began falling back to Earth.

According to Musk[0], a first stage of a rocket is judged by the energy it can impart to its payload at the standardized height of 100 km. Merely getting to 100 km is the easy part. The Falcon 9 is able to deliver 120 giga-joules to its payload at the height of 100 km, while performing a return to launch site landing. While it appears the New Shepard had ~0 joules left at 100 km.

[0] - http://www.spacex.com/news/2015/12/21/background-tonights-la...

[1] - https://www.blueorigin.com/news/news/blue-origin-makes-histo...

This really made the difference clear to me, thanks for the write up.

As @jzila pointed out this didn’t include the potential energy, with that included, the energy comparison becomes more stark.

The Falcon 9 v1.1 weights 557.6 tons and the number floating around for New Shepard is 40 tons. So that would give 496 gigajoules of potential energy for the Falcon 9 and 36 gigajoules of energy for New Shepard.

For a total of energy of 616 gigajoules for the Falcon 9 and 36 gigajoules for the New Shepard.

Amazing, thanks for that explanation.

Potential energy is energy, so it's not quite correct that New Shepard had 0 joules at 100km. At 100km and 0 velocity it'll have about 1 gigajoule of energy per metric ton of mass.

Potential energy is not energy that you can give to a payload unless you want to have it fall 100km back to earth.

Sure, but it's energy that a rocket needs to impart nevertheless.

The point was that the measurement is what it can impart on a payload (presumably one going UP.) So your point doesn't seem relevant.

I think the point was to illustrate the difference in energy requirements for the rocket to impart to the payload.

That said, re-reading Elon's article, he did explicitly say _kinetic_ energy in the 120GJ figure, in which case 0 is the right number for New Shepard at 100km.

Reply on news.ycombinator.com