Branson admits Virgin space mission was going the wrong direction • Hacker News Board

Re: Branson admits Virgin space mission was going the wrong direction

#21

Post by Retric » Fri, Mar 03, 2017, 5:01 PM UTC

Gravityloss wrote: post #8

saalweachter wrote: post #5

I must say - both physically compelled by the pun and because that it is a pun makes it no less true - that SpaceX has been a rousing success for the "launch and iterate" mantra so often pushed on HN. Having a product, that works, that people can pay you for, as soon as possible makes a huge difference, even if what you push out first is no where near what you want your finished product to be. The contrast to Virgin…

SpaceX looks like a software company that has had success with their product so far but is in the process of a major refactoring to a new technology base. Basically if they want to fly reusable rockets with high reliability and low refurbishment time and cost, they have to redesign and rebuild quite a lot. And they need new philosophies and processes. You can for example look at their current Merlin gas generator tec…

Projects are never going to pick the perfect solution out of the gate. But, tested compromises also have value.

I would suggest SpaceX freeze a design every 5-7 years that's good enough to scale while cheaper than it's completion and then have a more experimental path. If option A costs 20 million more, but has a 98+% success rate and option B saves 20 million then the market can chose which to focus on.

The real 'problem' spaceX is facing is humans simply don't send all that much stuff into space, so they are never get enough data get the experimental path stable.

Re: Branson admits Virgin space mission was going the wrong direction

#22

Post by pdonis » Fri, Mar 03, 2017, 5:45 PM UTC

rz2k wrote: post #14

bmcusick wrote: post #9

There's no indication that they've figured out that Virgin's real problem is their architecture. They're still trying to use wings to get to space. The Germans and NASA back in the 50s understood that "mass is mass", and wings compete with fuel for weight. They're dead mass you have to accelerate. The lift they provide isn't worth it. The Russians put Sputnik and Gegarin in orbit with a rocket. NASA went to the Moon…

Would you say that achieving orbit is a problem of achieving velocity more than lifting to a certain altitude, and that wings are a delicate tool for decelerating when coming back to earth?

> achieving orbit is a problem of achieving velocity more than lifting to a certain altitude

Yes, and this has been well understood for decades. The basic math is simple: per unit mass, the potential energy change required to get from the Earth's surface to orbital altitude (say 200 km, or 200,000 meters) is

gh = 9.8 * 200,000 = about 2 million Joules/kg

whereas the kinetic energy change required to get from rest on the rotating Earth, a speed of about 300 m/s at the latitude of the Kennedy Space Center, to orbital speed, 8000 m/s, is

1/2 (v2^2 - v1^2) = 1/2 (8000^2 - 300^2) = about 32 million Joules/kg

So the change in velocity dominates the energy requirement, which drives everything else.

Re: Branson admits Virgin space mission was going the wrong direction

#23

Post by nkoren » Fri, Mar 03, 2017, 5:58 PM UTC

bmcusick wrote: post #9

There's no indication that they've figured out that Virgin's real problem is their architecture. They're still trying to use wings to get to space. The Germans and NASA back in the 50s understood that "mass is mass", and wings compete with fuel for weight. They're dead mass you have to accelerate. The lift they provide isn't worth it. The Russians put Sputnik and Gegarin in orbit with a rocket. NASA went to the Moon…

This is true. All the space engineers I knew were saying, at the time, that scaling wings is a hell of a lot harder than scaling rockets. And it has been. Plus, air-launch introduces an extra element of operational complexity, and extra manufacturing complexity since you have two lines of hardware with very few synergies between them.

These problems could have been overcome, however. They would be left with a more complicated and expensive space-tourism system than is strictly necessary, but there's no reason it can't be done. Overcoming the limitations of their architecture, however, would have required good management. They haven't had that: a quick perusal of glassdoor shows that their management is driven by people whose core competency is back-scratching and accruing seniority, rather than a meritocracy driven by technical and managerial skill.

That problem, alone, has been more than sufficient to keep Virgin Galactic grounded. Bad management can kill even the most elegant, viable technology.

Re: Branson admits Virgin space mission was going the wrong direction

#24

Post by taylorexpander » Sat, Mar 04, 2017, 8:53 AM UTC

rz2k wrote: post #14

bmcusick wrote: post #9

There's no indication that they've figured out that Virgin's real problem is their architecture. They're still trying to use wings to get to space. The Germans and NASA back in the 50s understood that "mass is mass", and wings compete with fuel for weight. They're dead mass you have to accelerate. The lift they provide isn't worth it. The Russians put Sputnik and Gegarin in orbit with a rocket. NASA went to the Moon…

Would you say that achieving orbit is a problem of achieving velocity more than lifting to a certain altitude, and that wings are a delicate tool for decelerating when coming back to earth?

There is actually a term used in the field by engineers and scientists: "delta v." You might have heard Musk mention it a few times in his talks.

It's a measure of change in velocity (hence the delta… v…, and in mathematical terms is literally written with the symbol delta) required to reach or escape x orbit.

For example you need a delta v of approx 9.3 km/s to go from Earth to LEO. From LEO to GEO you'd need a delta v of roughly half of that. Engineers in this sense would talk about a total delta v budget of ~13 km/s and some change to achieve Earth to GEO.

The question is then how do you design a rocket that can produce those numbers? Higher delta v requirements means higher mass requirements. You'd need more propellant to produce that thrust, and more structure to house it and hardware to control it. At some point it simply doesn't work anymore because it becomes counter intuitive to keep adding more mass.

Enter the concept of staging. Staging allows you to discard your useless mass after it's done it's job. For example you might need 9.3 km/s to achieve LEO, but you might also know it's not a linear relationship so that you need more of that upfront and less of it later. In that case, rocket engineers simply designed around that and created heavy first lift stages to produce the bulk of that delta v, and then discarding the heavy structure and hardware after the propellant has been exhausted.