ALTIUS SPACE MACHINES – All Information Proprietary and Confidential

Some Physics and Market Implications of Propellant Depots

for BEO Transportation

Jonathan GoffPresident/CEOAltius Space Machinesjongoff@altius-space.com

Space Show Classroom DiscussionApril 5th 2011

ALTIUS SPACE MACHINES 2

“If we are serious about this, then our objective must be more than a disconnected series of missions, each conducted at huge expense and risk, and none building a lasting infrastructure to reduce the expense and risk of future operations. If we are serious, we will build capability, not just on the ground but in space. And our objective must be to make the use of space for human purposes a routine function.

Exploration that is not in support of something else strikes me as somehow selfish and unsatisfying, and not consistent with the fact that we are using public funds for this enterprise, no matter how small a fraction of the total budget they may be.

If the architecture of the exploration phase is not crafted with sustainability in mind, we will look back on a century or more of huge expenditures with nothing more to show for them than a litter of ritual monuments scattered across the planets and their moons.”

OSTP Director John MarburgerGoddard Memorial Symposium

March 7, 2008

ALTIUS SPACE MACHINES 3

Depots as a Market Driver (1 of 3)• One of the key challenges facing most proposed low-cost

space transportation options is lack of a clear market with high fligt rate demand– RLVs, gun launch options, and other exotica all require ~30-50

launches per year to close their business case– Most existing markets not sufficiently elastic at prices >$1k/lb to

enable that flight rate for even one launcher• While the engineering is daunting, most low-cost launch

projects fail in the fund-raising phase, not execution (Kistler only real exception)

• If the market/business case were clear, it would be easier to attract private investment into low-cost launch development

• Only way to break out of the zero-sum game of NASA budgets

ALTIUS SPACE MACHINES 4

Depots as a Market Driver (2 of 3)• Only three markets likely to provide the needed levels of flight

demand:– People– Provisions– Propellants

• Attributes:– Small minimum payload size (high divisibility)– Short lead times for payload production/integration (self loading

cargo, gas tank fillup)• Propellant-specific benefits:

– No need for man-rating– Low inherent payload value– High volumes required for even modest BEO exploration

ALTIUS SPACE MACHINES 5

Depots as a Market Driver (3 of 3)

• Depots can serve as a market driver if the following conditions are met:

1. Sufficient demand for BEO transportation2. Low enough cost development/operations of

depot capabilities3. Orbital Dynamics challenges can be overcome

for the desired depot-utilizing missions4. Lower-cost, lower-hassle, lower-risk rendezvous

and docking

ALTIUS SPACE MACHINES 6

Depot Orbital Mechanics Challenges (1 of 4)

• For LEO depot to lunar travel, orbital mechanics are not a big challenge– Launch when your depot’s orbital plane crosses the point

the Moon would be at when you would get there– Nodal Regression (5-7deg/day) plus lunar relative motion

(360 deg/28 days = ~13deg/day) work together to give departures every ~9-10 days

– Assuming precision landing/hazard avoidance technologies, this enables 2-3 lunar departures/returns per month per depot plane

– Bottom line: It would be nice to be flying enough that 3 missions per month was an actual impediment

ALTIUS SPACE MACHINES 7

Depot Orbital Mechanics Challenges (2 of 4)

• For departures beyond cislunar space, orbital mechanics are more challenging

• For optimal departure to a given target, you need to depart earth’s Sphere of Influence with a specific velocity vector– Patched Conics Theory and Pork Chop Plots– The period of minimal departure delta-V is often short, often less than

2 weeks– Nodal regression only lines up the depot orbital plane with a given

departure vector every 180 deg / 5-7 deg/day = ~25-35 days for a LEO depot and 180 deg/ 13 deg/day = ~14 days for a L1/L2/LUNO depot

– Easy to setup a single-use LEO depot so that at the planned departure window the plane and vector line up, but odds are it won’t be lined up right for the next target.

– Lunar vicinity depots have other challenges…

ALTIUS SPACE MACHINES 8

Depot Orbital Mechanics Challenges (3 of 4)

• The departure vector (“departure asymptote”) often has a large component out of the plane of the ecliptic– May require injection burn to be performed at latitudes far

from the equator (“latitude of the perigee”)– For circular depot orbits not a problem so long as

inclination is greater than required departure latitude– For depots in elliptical orbit requires correct alignment of

the major axis to avoid penalties– Earth swingby departures from L1/L2 may not give

sufficient flexibility in “latitude of the perigee” for many departure trajectories

ALTIUS SPACE MACHINES 9

Depot Orbital Mechanics Challenges (4 of 4)

• Summary:– Unadjusted circular LEO depot orbits of sufficient

inclination only have a 30-50% chance of lining up with a given departure target

– Easy to do single-use depots, harder to reuse the depot

– L1/L2 swingby departures more likely to have the planes align, but may have issues with latitude of the perigee

ALTIUS SPACE MACHINES 10

Potential Depot Orbital Mechanics Solutions (1 of 3)

• There are some possible solutions• Potential Solution #1: Multiple LEO Depots (Brute Force)

– If you build multiple depots in the same inclination but different, evenly spaced planes, you are more likely to have one of them align with any given departure opportunity

– If optimal departure window is 7 days you need (25 to 35 days / 7 days = 4-5 depots)

– If optimal departure window is 14 days you need 2-3 depots• Benefits:

– Depots can be in resonant orbits and don’t require special maneuvering• Issues/Requirements:

– Requires depots to be inexpensive– Means some depots may be idling– LEO departure (instead of departing from HEO or L1/L2) requires larger depots– More likely to require long storage times (either more aggressive boiloff design

required or higher losses)

ALTIUS SPACE MACHINES 11

Potential Depot Orbital Mechanics Solutions (2 of 3)

• Potential Solution #2: Depot Orbital Phasing– A small burn can place the depot into an elliptical orbit with a different

nodal regression rate• Lower perigee (faster regression) or raise apogee (slower regression)

– If started far enough in advance, can allow depot plane to line up with arbitrary vector

– Rough calculations indicate that 6 months or less may be feasible for “repositioning” a depot

• Benefits: Only one depot required so long as < 2 BEO departures/yr

• Issues/Requirements:– Requires depot to be capable of modest maneuvering– Lowering perigee is hard, so most likely raising apogee– Imposes additional delivery costs to raise apogee– Hard/impossible to do while maintaining a resonant orbit, means

launch ops and timing more variable

ALTIUS SPACE MACHINES 12

Potential Depot Orbital Mechanics Solutions (3 of 3)

• Potential Solution #3: High/Low Depots– Place one depot into a HEO that will arrive at the right orientation in time for a

given departure– Use one or more LEO depots to send tankers to HEO depot every time planes

line up (about once per month per depot)– Depending on mission element size, launch directly to HEO depot and refuel,

or visit LEO depot first then go to HEO depot then depart– To reuse HEO depot, use propulsive or aerobraking back to LEO after mission

• Benefits: – Only two depots required (though more help)– Departure from a point with 2.5-3km/s “already behind you” enables smaller

depot or bigger departure missions– One LEO depot can service multiple HEO depots at the same time

• Issues/Requirements:– HEO depot requires substantial maneuvering capability (ULA simple depot

with plumbing to do return burn?)– Penalty for HEO depot emplacement and return

ALTIUS SPACE MACHINES 13

Lower Cost, Lower Hassle, Lower Risk Rendezvous and Docking • High tempo propellant deliveries

also require significant improvements in rendezvous and docking technologies– Current prox-ops approaches too

risky for large numbers of dockings

• A single year of depot operations may eventually require more rendezvous and docking ops than in all of human history to-date

• Altius Space Machines is working with SRI International and NASA on an Electroadhesive Sticky-Boom non-cooperative rendezvous and docking solution that may help simplify this challenge.