does that mean that it has to enter the atmosphere and land at the moment of arrival, irrespective of weather conditions at the landing site
Changing landing sites may not be easy or possible with a late decision. The time and direction of arrival are pretty much fixed. Braking into orbit and then refueling may be a real possibility.
Quote from: guckyfan on 07/29/2018 03:16 pmChanging landing sites may not be easy or possible with a late decision. The time and direction of arrival are pretty much fixed. Braking into orbit and then refueling may be a real possibility.In fact, braking into orbit may be preferable for many reasons. Including doing a thorough inspection of the state of the heatshield prior to re-entry. Does BFS carry sufficient fuel upon a Mars return journey to brake into Earth orbit?
Quote from: M.E.T. on 07/29/2018 03:51 pmQuote from: guckyfan on 07/29/2018 03:16 pmChanging landing sites may not be easy or possible with a late decision. The time and direction of arrival are pretty much fixed. Braking into orbit and then refueling may be a real possibility.In fact, braking into orbit may be preferable for many reasons. Including doing a thorough inspection of the state of the heatshield prior to re-entry. Does BFS carry sufficient fuel upon a Mars return journey to brake into Earth orbit?They won't have anywhere near enough propellant for propulsive braking. They still need to shed the interplanetary speed with the heat shield and do a perigee raising burn to stay in orbit.I don't know enough about trajectories. Maybe they could brake into EML-1 or 2 with little propellant as an emergency measure. But that would be very inconvenient for efficient normal operation. Would probably only work on a slow Hohmann transfer. SpaceX wants faster trajectories.
How deep would you have to dive into atmosphere for going into high elliptical orbit with aerobraking ?
Quote from: M.E.T. on 07/29/2018 12:10 amdoes that mean that it has to enter the atmosphere and land at the moment of arrival, irrespective of weather conditions at the landing siteThere is a related problem in long-range commercial aviation. They can't confidently know that weather (or even runway availability) at the intended destination will permit landing on arrival, and they don't have nearly enough spare fuel to just circle until things get better for a significant fraction of cases. The accepted solution in that aviation is alternate landing sites, all reachable on original trip fuel (though not necessarily reachable if the decision is made too late).I'll wager Mars operations will entail _not_ orbiting Earth on return, but will include at least one alternate landing site, maybe more. Holding down excess fuel requirement would mean making the divert decision a ways out.
Direct quote from the NET:QuoteThis is the Launch Director on the countdown NET. Called a hold for an issue with our droneship. Unable to maintain power to allow us to proceed with launch on time, and we simply ran out of time. At this point we're proceeding with propellant offload. Once we complete that and TEA/TEB sweeps, we'll prepare to lower the vehicle. And we'll address a helium leak on the second stage QD interface. And we'll set up for a 24 hour recycle.
This is the Launch Director on the countdown NET. Called a hold for an issue with our droneship. Unable to maintain power to allow us to proceed with launch on time, and we simply ran out of time. At this point we're proceeding with propellant offload. Once we complete that and TEA/TEB sweeps, we'll prepare to lower the vehicle. And we'll address a helium leak on the second stage QD interface. And we'll set up for a 24 hour recycle.