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ULA ACES or a large LCH4 stage for Pluto and Ice Giant orbital missions

March 4, 2018


We examine the OPAG technology papers presented at the February 2018 meeting in Virginia

Up first is Elliot Pluto on entering Pluto orbit with a 400 Kg dry mass payload and killing 10 Km/s after a 15-year flight time ( page 5)


For comparison, New Horizons flew by Pluto at 14 Km/s with a shorter TOF.  From Elliott;


Assuming ~400 kg dry mass (New Horizons) s/c

◦ Monoprop (Isp~230 s) would require >33,000 kg of propellant

◦ SRM (Isp~290 s) would require ~13,000 kg

◦ BiProp (Isp~320 s) would need ~9300 kg

◦ H2/O2 (Isp~450 s) would need ~3500 kg Adding propulsion system mass to s/c dry mass quickly pushes all chemical options out of range of feasibility”

End of Quote

Elliot and JPL think the chemical is not feasible, however with ULA distributed launch or a large LCH4 stage refueled on orbit means you have greater through weight also Elliot states on page 9 of this presentation Elliott-Ice

JPL study group suggests the need for a new LH2/LO2 engine since they are sizing the engine and propellant tank mass to their payload but perhaps this engine already exists? The ULA ACES gasses H2/O2 engine could be clustered and the 3500 Kg of LH2/LO2 could be vaporized with a heater, this, however, brings about a thought, If ACES is heading towards Pluto at 10 Km/s and cannot kill that speed then perhaps staging is the answer? ACES separates and a smaller LH2/LO2 stage does the rest of the job

Elliot Et al might be making other assumptions in regards to LH2/LO2 stages such as the stage are not fully fueled at TNI?

Elliot Et al suggests future studies of hybrid chemical aerobraking but also we have suggested on these pages LXe cooled by LH2 in a hybrid SEP chemical system

EDIT 8 March 2018

We use several online rocket equation calculators to find for stoping ULA ACES at Pluto by bleeding off 11 kilometers per second with a 15 year flight time, none of them close for an ACES orbital mission


we did another one with a 1000 Kg payload twice what Elliot calls for

worksheet (1)

ULA ACES wet and dry mass at 74 M/t and 6 M/t are educated guesses from space launch report


However, Elliot seems to indicate in the JPL report above utilizing a Titan aerobraking but this would add to the 15-year timeline or not? Even so, a slower flyby mission to that of New Horizons would yield a longer loiter time at Pluto IE a 3 k/s flyby.

It appears a 67 Mt ACES could put itself into Neptune orbit with its 7-ton dry mass

Earth Neptune arrival Delta V

Perhaps a Cryogenic Xenon SEP system embedded in the ULA ACES could provide that 2 to 3 Km/s difference? After all, Elliot asks if there is a commercial or exploration use for LH2/LO2 systems and the answer is yes.Utilizing SEP to preposition chemical propellents is not a new idea and we like the idea of hybrid chemical SEP tugs for cislunar space economy.LXe is cryocooled in a low mass tank by the ACES LH2

Next post

Human and science mission directorates jointly fund with the DOD/NRO a 4-way competitive fly off

Cislurnar & deep space tug

two bids each chosen for SEP and chemical tugs

submissions encouraged for hybrid systems involving homogenous and heterogeneous systems

all Tugs should be able to dock with the others in order to provide staging









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