8 ms·

An Inside Look: SpinLaunch Flight Test #7

12 points by dangle1 4y ago

Gravityloss 4y ago
Their full scale production release speed would be 2 km/s. And as far as I understood, this test now was 500 m/s. Already supersonic, since speed of sound at sea level is 340 m/s. Great! Orbital velocity is over 7 km/s, but because of various losses, rockets usually need about 10 km/s of delta vee. So this would need to be a full blown rocket anyway, spin launch would just give assist to it. Spin launch would greatly reduce gravity losses but would probably greatly increase drag losses because of the high speed at low altitude. Haters are going to hate, but it's great to see them do actual tests.
- panick21_ 4y ago
  That's what I don't get. Their rocket is still a 2 stage rocket that is not much lighter, different or easier to construct then other small scale launcher. But in comparison to those, their fix cost are way higher. In addition to all the difficulty of rocket itself they have to solve a whole other set of unrelated problems.
  - Gravityloss 4y ago
    Well, increasing delta vee increases mass rate exponentially, which leads to unexpected effects. initial_mass / final_mass = exp(delta vee / exhaust velocity). This assumes a single stage to orbit rocket for simplicity. So the mass ratio for a delta vee of 10 km/s and exhaust velocity of 3 km/s might be exp(10/3) = exp(3.33) = 28. So for 1000 kg of fueled rocket, you have 35 kg of empty rocket + payload. Rocket structure might be 25 kg and payload might be maybe 10 kg. If you can shave off 1 km/s off with spin launch assist, your mass ratio will be exp(9/3) = exp(3) = 20. For a 1000 kg of fueled rocket, you have 50 kg for rocket structure + payload. If the rocket structure is still 25 kg, your payload is now 25 kg. Your payload just multiplied by 2.5x with this insignificant-looking 10% ground assist. In reality of course it's more complex with two stages. And making the rocket resistant to side forces and high drag forces can increase its weight.
    - panick21_ 4y ago
      But in practice they use very inefficient engines and still require 2 stages. This leads to their rocket being the same weight for about the same payload as their competitors. So I guess the question on can ask, whats easier, building a electric powered rocket engine like the Rutherford or building a gigantic electric launch platform. It also imposes a number of requirements on that rocket structure and the flexibility payload volume. Many payloads are volume limited and most rockets eventually want to have extended fairings, this will be very difficult for them. Even if they improve their engine performance overtime, it will be practically difficult to actually launch bigger and heavier payloads if you can't increase the volume very much.

12 points by dangle1 4y ago

Their full scale production release speed would be 2 km/s. And as far as I understood, this test now was 500 m/s. Already supersonic, since speed of sound at sea level is 340 m/s. Great! Orbital velocity is over 7 km/s, but because of various losses, rockets usually need about 10 km/s of delta vee. So this would need to be a full blown rocket anyway, spin launch would just give assist to it. Spin launch would greatly reduce gravity losses but would probably greatly increase drag losses because of the high speed at low altitude. Haters are going to hate, but it's great to see them do actual tests.

panick21_ 4y ago
That's what I don't get. Their rocket is still a 2 stage rocket that is not much lighter, different or easier to construct then other small scale launcher. But in comparison to those, their fix cost are way higher. In addition to all the difficulty of rocket itself they have to solve a whole other set of unrelated problems.
- Gravityloss 4y ago
  Well, increasing delta vee increases mass rate exponentially, which leads to unexpected effects. initial_mass / final_mass = exp(delta vee / exhaust velocity). This assumes a single stage to orbit rocket for simplicity. So the mass ratio for a delta vee of 10 km/s and exhaust velocity of 3 km/s might be exp(10/3) = exp(3.33) = 28. So for 1000 kg of fueled rocket, you have 35 kg of empty rocket + payload. Rocket structure might be 25 kg and payload might be maybe 10 kg. If you can shave off 1 km/s off with spin launch assist, your mass ratio will be exp(9/3) = exp(3) = 20. For a 1000 kg of fueled rocket, you have 50 kg for rocket structure + payload. If the rocket structure is still 25 kg, your payload is now 25 kg. Your payload just multiplied by 2.5x with this insignificant-looking 10% ground assist. In reality of course it's more complex with two stages. And making the rocket resistant to side forces and high drag forces can increase its weight.
  - panick21_ 4y ago
    But in practice they use very inefficient engines and still require 2 stages. This leads to their rocket being the same weight for about the same payload as their competitors. So I guess the question on can ask, whats easier, building a electric powered rocket engine like the Rutherford or building a gigantic electric launch platform. It also imposes a number of requirements on that rocket structure and the flexibility payload volume. Many payloads are volume limited and most rockets eventually want to have extended fairings, this will be very difficult for them. Even if they improve their engine performance overtime, it will be practically difficult to actually launch bigger and heavier payloads if you can't increase the volume very much.