Tales of the Groundbound: Scimon and the Mün, Chapter 9

[steuben]

Chapter 9

Gus, Bob, Linus, and Aldald stood in the design hall. They were looking at the full sized blueprints of a probe on one of the walls. The science and engine sections were broken out into other blueprints elsewhere on the wall. On a table in one corner was a paper model of the probe and launcher.

“We’ll leave aside the launcher for the moment,” Aldald said as he pushed up his glasses. “It is sufficient to get Scimon, and its up fueled variant, to an eighty by eighty orbit. Upon achieving orbit, Scimon will separate from the launcher. From orbit Scimon will perform a burn to enter a Münar flyby with a periapsis of twenty kilometers with a Kerbin free-return trajectory. Projected Kerbin periapsis will be forty kilometers. Upon entry to the atmosphere it will burn the remaining fuel and aero brake until airspeed is reduced to 250 mps. The parachutes will deploy bringing it to rest on the surface.”

Gus looked at the model in the corner. “What’s the projected reliability?”

Aldald pushed up his glasses. “For the launcher we are projecting 4 nines. For Scimon it is only two nines.”

Gus and Bob frowned.

“Most of the failure modes and uncertainty are a result of a lack of information about how propulsion and control will behave in Münar orbit,” Aldald continues. ”Re-entry to Kerbin also presents large amounts of uncertainty, despite our performance so far with the tourist contracts.”

“Where’s the uncertainty in the control systems,” Linus said. “I thought the commands were all relayed from here to Scimon.”

“They are,“ Aldald said. “The problem is the relay itself. There is concern that the conditions either on launch or in transit will affect the forward or back channels.”

“What about a second set of radio equipment,” Bob asked.

Linus shook his head. “Too much mass.”

“Correct,” Aldald said. “In the event of failure of one of the channels, Scimon will attempt to use the remaining channel for both directions. If both channels fail after the exit burn, Scimon will still have a return trajectory to Kerbin. This will be sufficient to reduce speed enough for landing after two passes. The parachutes will automatically deploy once it is at a safe speed and appropriate altitude.”

“No readings will be taken in the event of total radio failure,” Bob asked.

“In that situation Scimon is set to automatically take four equally spaced samples,” Aldald said. “It will start at periapsis up to 2000 km on the outbound portion of the flyby.”

“And all of that is less that a second set of radios?” Linus said.

“Yes. Those automation systems mass approximately 50 percent less.”