Monday, September 28, 2015

Early days - asteroid redirect (2/4)

This is a follow-on to the previous post describing carrier spacecraft. I know asteroid retrieval has its haters and certainly compared to the goals of the Constellation program it sounded like a major letdown, but if you dig into the data it starts making sense. Here's my take on an aggressive capture program:

Asteroid Redirect Program

This is essentially the NASA ARM program described by the 2012 Keck Institute report, with some modifications. First, deployable microsatellites will be used to bag targets (including loose concretions or binaries). Second, a tether-based solution will be used to despin targets (saving about 500kg fuel). These two factors together allow a much broader range of targets to be captured. Third, the program will be considered an ongoing project to accumulate mass in Lunar orbit rather than a one-shot mission to grab a single target. The program will benefit from the carrier program by gaining high-power in-space radar observation of targets, reliable on-orbit assembly of mass-efficient solar arrays and multiple onboard microsatellites for redundancy and safety.

Another major difference: use of a Falcon 9H allows the entire 15.5t vehicle to be launched into Lunar transfer orbit, saving 5-6km/s of dV(~3.5t fuel), two years of travel time and avoiding an extended spiral through the Van Allen belts. At an Isp of 3000 and a relocation budget of 200m/s dV, fuel mass is only 0.68% of the target’s mass (146.6 to 1). The craft’s ~8t of fuel could capture up to 1,170t of target. Using the study’s 160m/s figure the fuel mass is only 0.55% (183.3 to 1) and the target mass is as high as 1,460t. Target 2000 SG344 could return 1,800 to 3,600 tons in less than three years due to its very favorable orbit; other such targets are waiting to be found.
A launch in 2018 could yield a return as early as 2023 (400 tons) to 2026 (1,300 tons). If we average 700 tons per target, six launches over 2018-2023 could return 4,200 tons over 2025-2031. That’s ten times the mass of the ISS for 4% of the cost.
Program DDT&E: $1,100m
Vehicles: $330m each, $1,980m total
NASA costs: $616m (grants,
Operations: $175m
Launch: $900m
Margin: $1,430m
Program duration: 2016-2031 (15 years)
Program total: $6,200m ($413m per year)
Recoverable costs: ~$1m to $2.5m per ton of material; from $0 up to $4.2b to $10.5b
Alternate scenario: DDT&E drops by half and vehicles drop to $150m due to carrier program cooperation. Costs become $550m, $900m, $325m, $175m, $900m, $855m; total of $3,705m or $247m per year. ‘Access fee’ of $1,000/kg yields recoverable costs up to 113% of program costs.

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