The technologies that were developed for this program, some of which are still being refined, include:1 - restartable ignition system for the first-stage booster. Restarts are required at both supersonic velocities in the upper atmosphere—in order to decelerate the high velocity away from the launch pad and put the booster on a descent trajectory back toward the launch pad—and at high transonic velocities in the lower atmosphere—in order to slow the terminal descent and to perform a soft landing. 2 - new attitude control technology—for the booster stage and second stage—to bring the descending rocket body through the atmosphere in a manner conducive both to non-destructive return and sufficient aerodynamic control such that the terminal phase of the landing is possible.This includes sufficient roll control authority to keep the rocket from spinning excessively as occurred on the first high-altitude flight test in September 2013, where the roll rate exceeded the capabilities of the booster attitude control system (ACS) and the fuel in the tanks "centrifuged" to the side of the tank shutting down the single engine involved in the low-altitude deceleration maneuver. The technology needs to handle the transition from the vacuum of space at hypersonic conditions, decelerating to supersonic velocities and passing through transonic buffet, before relighting one of the main-stage engines at terminal velocity. 3 - hypersonic grid fins were added to the booster test vehicle design beginning on the fifth ocean controlled-descent test flight in 2014 in order to enable precision landing. Arranged in an "X" configuration, the grid fins control the descending rocket's lift vector once the vehicle has returned to the atmosphere to enable a much more precise landing location. 4 - throttleable rocket engine technology is required to reduce engine thrust because the full thrust of even a single Merlin 1D engine exceeds the weight of the nearly empty booster core. 5 - terminal guidance and landing capability, including a vehicle control system and a control system software algorithm to be able to land a rocket with the thrust-to-weight ratio of the vehicle greater than one, with closed-loop thrust vector and throttle control 6 - navigation sensor suite for precision landing7 - a large floating landing platform in order to test pinpoint landings prior to receiving permission from the US government to bring returning rocket stages into US airspace over land. 8 - large-surface-area thermal protection system to absorb the heat load of deceleration of the second stage from orbital velocity to terminal velocity9 - lightweight, deployable landing gear for the booster stage.
B - what would be the main roadblocks ? computing power maybe ?
Quote from: Archibald on 02/20/2018 07:07 amB - what would be the main roadblocks ? computing power maybe ?I'd say that's probably a good bet.Precision landing could also have been an issue, although I don't know how precise you can get without GPS and only using radio beacons (?) and IMUs. Probably not precise enough to nail a barge in the ocean, but a large-ish landing pad could be workable.
Third is computing power, or rather, lack of computing power. Not just for the rocket but for simulating the environment as well..
The first of which is the fact that the H-1 engine was unable to throttle.Second thing is that the thrust of a single H-1 is twice of what is required to hover the empty mass of a S-IB stage. So, substantial hover-slam required to get the stage on the ground.
Didn't SpaceX start with the Saturn 1 recovery concepts when they first started? Parachute based recovery....
... later the RS-27 was evolved into the RS-56....
Quote from: Lobo on 02/20/2018 10:05 pm... later the RS-27 was evolved into the RS-56....What was the RS-56?
How about a recovery scheme where the first stage turns around while in space using gas thrusters, restarts some engines for an entry burn, deploys some sort of air break at the top to keep it pointed the right way, then uses parachutes to splash down? That would avoid the issues of developing the computers for guidance, control surfaces, and throttleable H-1s which may not have been easily done in the 1960s.
Immediately after separation, the first stage would have deployed from its base a 217-foot-wide "ring-shaped ribbon parachute" made of steel mesh. At its deployment altitude, air resistance would be minimal, so stage and parachute would continue to coast upward to an altitude of about 40 miles before turning nose-down and falling toward the ocean. The conical blast shield would help to protect it from aerodynamic heating during descent.It would attain a descent velocity of 150 feet per second by the time it fell to 150 feet above the water. At that moment, small solid-propellant motors would have ignited and burned for two seconds, gently lowering the first stage into the sea 189 miles downrange of the launch site.A large recovery ship, pre-positioned to collect the stage, would soon have arrived. Von Braun envisioned it as a specialized "seagoing drydock," which would have filled on-board tanks with sea water to submerge, moved its drydock section under the bobbing first stage, then pumped seawater from its tanks to raise the stage clear of the ocean. The ship would then have set course for a special harbor close to the launch site where the first stage would be inspected, refurbished, and reused. The same harbor would, von Braun noted, serve ocean-going ships that would deliver thousands of tons of propellants to the launch site.
Each craft was planned to slow to about 110 m/s (4% of speed before retrofire) by a main solid fuel retrorocket, which fired for 40 seconds starting at an altitude of 75.3 km above the Moon, and then was jettisoned along with radar unit at 11 km from the surface. The remainder of the trip to the surface, lasting about 2.5 minutes, was handled by smaller doppler radar units and three vernier engines running on liquid fuels fed to them using pressurized helium. (The successful flight profile of Surveyor 5 was given a somewhat shortened vernier flight sequence as a result of a helium leak). The last 3.4 meters to the surface was accomplished in free fall from zero velocity at that height, after the vernier engines were turned off. This resulted in a landing speed of about 3 m/s. The free-fall to the surface was in an attempt to avoid surface contamination by rocket blast.