MIT team proposes storing extra rocket fuel in space for future missions

By Jennifer Chu, MIT News Office

Future lunar missions may be fueled by gas stations in space, according to MIT engineers: A spacecraft might dock at a propellant depot, somewhere between the Earth and the Moon, and pick up extra rocket fuel before making its way to the lunar surface.

Orbiting way stations could reduce the fuel a spacecraft needs to carry from Earth — and with less fuel onboard, a rocket could launch heavier payloads, such as large scientific experiments.

Over the last few decades, scientists have proposed various designs, such as building a fuel-manufacturing station on the Moon and sending tankers to refill floating depots. But most ideas have come with hefty price tags, requiring long-term investment.

The MIT team has come up with two cost-efficient depot designs that do not require such long-term commitment. Both designs take advantage of the fact that each lunar mission carries a supply of “contingency propellant” — fuel that’s meant to be used only in emergencies. In most cases, this backup fuel goes unused, and is either left on the Moon or burned up as the crew re-enters the Earth’s atmosphere.

Instead, the MIT team proposes using contingency propellant from past missions to fuel future spacecraft. For instance, as a mission heads back to Earth, it may drop a tank of contingency propellant at a depot before heading home. The next mission can pick up the fuel tank on its way to the Moon as its own emergency supply. If it ends up not needing the extra propellant, it can also drop it at the depot for the next mission — an arrangement that the team refers to as a “steady-state” approach.

A depot may also accumulate contingency propellant from multiple missions, part of an approach the researchers call “stockpiling.” Spacecraft heading to the Moon would carry contingency propellant as they normally would, dropping the tank at a depot on the way back to Earth if it’s not needed; over time, the depot builds up a large fuel supply. This way, if a large lunar mission launches in the future, its rocket wouldn’t need a huge fuel supply to launch the heavier payload. Instead, it can stop at the depot to collect the stockpiled propellant to fuel its landing on the Moon.

“Whatever rockets you use, you’d like to take full advantage of your lifting capacity,” says Jeffrey Hoffman, a professor of the practice in MIT’s Department of Aeronautics and Astronautics. “Most of what we launch from the Earth is propellant. So whatever you can save, there’s that much more payload you can take with you.”

Hoffman and his students — Koki Ho, Katherine Gerhard, Austin Nicholas, and Alexander Buck — outline their depot architecture in the journal Acta Astronautica.

Pickup and drop-off in space

The researchers came up with a basic mission strategy to return humans to the Moon, one slightly different from that of the Apollo missions. During the Apollo era, spacecraft circled close to the lunar equator — a route that required little change in direction, and little fuel to stay on track. In the future, lunar missions may take a more flexible approach, with the freedom to change course to explore farther reaches of the Moon — such as the polar caps, for evidence of water — a strategy that would require each spacecraft to carry extra fuel to change orbits.

Working under the assumption of a more global exploration strategy, the researchers designed a basic architecture involving a series of stand-alone missions, each exploring the surface of the Moon for seven to 14 days. This mission plan requires that a spacecraft returning to Earth must change its orbital plane when needed. Under this basic scenario, missions could operate under existing infrastructure, without fuel depots, meaning that each spacecraft would carry its own supply of contingency propellant.

The researchers then drew up two depot designs to improve the efficiency of the basic scenario. In both designs, depots would be stationed at Lagrange points — regions in space between the Earth, Moon, and sun that maintain gravitational equilibrium. Objects at these points remain in place, keeping the same relative position with respect to the Earth and the Moon.

Hoffman says that ideally, transferring fuel between the depot and a spacecraft would simply involve astronauts or a robotic arm picking up a tank. The alternative — siphoning fuel from tank to tank like you would for your car — is a bit trickier, as liquid tends to float in a gravity-free environment. But, Hoffman says, it’s doable.

“In building the International Space Station, every time a new module is added, we’ve had to hook up new fluid connections,” Hoffman says. “It’s not a trivial design problem, but it can be done.”

‘Creating value … against political uncertainty’

The main drawbacks for both depot designs include maintenance; keeping depots within the Lagrange point; and preventing a phenomenon, called “boil-off,” in which fuel that’s not kept at cold-enough temperatures can boil away. If scientists can find ways around these challenges, Hoffman says, gas stations in space could be an efficient way to support large lunar explorations.

“One of the problems with large space programs is, you invest a huge amount in building up the infrastructure, and then a program gets canceled,” Hoffman says. “With depot architectures, you’re creating value which is robust against political uncertainty.”

The paper came out of two MIT classes taught by Hoffman: 16.851 (Satellite Engineering) and 16.89 (Space Systems Engineering), in which students also looked at redesigning a lunar lander and evaluated different approaches to landing on the Moon.

James Head, a professor of geological sciences at Brown University, says the group’s two approaches optimize the possibility of both near-lunar missions and more ambitious, longer-duration missions to more distant destinations.

“Currently, NASA is once again considering circumlunar human operations and developing architectures for moving on to Mars,” Head says. “So this paper is extremely important and timely in the context of developing NASA plans for human exploration beyond low Earth orbit.”

See also on the NSS website: Orbital Propellant Depots: Building the Interplanetary Highway.

First Falcon Heavy Launch Delayed Until Next Year

Aviation Week reports:

Although it was initially slated to debut this year, SpaceX founder, CEO and Chief Designer Elon Musk says the company’s production schedule is too tight to support a test flight of the heavy-lift rocket from Vandenberg AFB, Calif., in 2014.

“We need to find three additional cores that we could produce, send them through testing and then fly without disrupting our launch manifest,” Musk said in a Feb. 20 interview. “I’m hopeful we’ll have Falcon Heavy cores produced approximately around the end of the year. But just to get through test and qualification, I think it’s probably going to be sometime early next year when we launch.”

Elon Musk’s Plans for Mars

From CBS This Morning: 2-minute video after 30-second advertisement.

Transcript after about 40 seconds:

“We’ve got to restore American ability to transport astronauts with domestic vehicles, and that’s what we hope to do in about two years.

“The next step beyond that is to maybe send people beyond low Earth orbit to a loop around the Moon, possibly land on the Moon — although I’m not super interested in the Moon personally because obviously we’ve done that and we know we can — but maybe just to prove the capability.

“Then we need to develop a much larger vehicle which would be sort of what I call a large colonial transport system. This would really be — we’re talking about rockets on a scale, a bigger scale than has ever been done before, that make the Apollo Moon rocket look small. And they would have to launch very frequently as well.

“That’s what’s needed in order to send millions of people and millions of tons of cargo to Mars, which is the minimum level to have a self-sustaining civilization on Mars.

“We might be able to complete that [rocket] in about 10 or 12 years, and hopefully the first people we’d send to Mars would be around the middle of the next decade.”

National Space Society Congratulates SpaceX on First Successful GEO Transfer Mission

The Washington DC-based National Space Society (NSS) congratulates Space Exploration Technologies (SpaceX) on the successful launch of the SES-8 telecommunications satellite. It was launched Tuesday, December 3, 2013 from Space Launch Complex 40 (SLC-40) at the Cape Canaveral Air Force Station at 5:41 PM Eastern Time.

The SES-8 is a GEOStar-2 satellite built by Orbital Sciences. The hybrid Ku- and Ka-band spacecraft weighs 3,138 kg (6,918 lbs) and will provide communications coverage of the South Asia and Asia Pacific regions.

This is the first mission to geo-synchronous orbit for SpaceX, and the second flight of the Falcon 9 v1.1. The upgraded version of the Falcon 9 has 60% more thrust than the Falcon 9 v1.0, and can loft payloads of up to 4,950 kg (10,690 lb) to geostationary transfer orbit.

Bruce Pittman, NSS Senior Vice President, said, “This milestone injects a new US competitor into the international commercial satcom launch market, and is an important step toward lowering the cost of access to space, which in turn will help drive space development and settlement.”

This flight of the Falcon v1.1 represents a major step forward commercially for SpaceX, and also demonstrates progress toward the certification of the Falcon 9 for Department of Defense payloads. Critical to geostationary transfer missions, for the first time the upgraded Falcon 9 second stage re-ignited for a 5-minutes 20-seconds burn to put the SES-8 into the correct orbit. SES is the world’s second largest telecommunications satellite company, fielding 54 geostationary satellites.

SpaceX Successfully Completes First Mission to Geostationary Transfer Orbit

Space Exploration Technologies (SpaceX) has successfully completed its first geostationary transfer mission, delivering an SES-8 satellite to its targeted 295 x 80,000 km orbit.  Falcon 9 executed a picture-perfect flight, meeting 100% of mission objectives.

Falcon 9 lifted off from Space Launch Complex 40 (SLC-40) at 5:41 PM Eastern Time on December 3.  Approximately 185 seconds into flight, Falcon 9’s second stage’s single Merlin vacuum engine ignited to begin a five minute, 20 second burn that delivered the SES-8 satellite into its parking orbit. Eighteen minutes after injection into the parking orbit, the second stage engine relit for just over one minute to carry the SES-8 satellite to its final geostationary transfer orbit.  The restart of the Falcon 9 second stage is a requirement for all geostationary transfer missions.

“The successful insertion of the SES-8 satellite confirms the upgraded Falcon 9 launch vehicle delivers to the industry’s highest performance standards,” said Elon Musk, CEO and Chief Designer of SpaceX.   “As always, SpaceX remains committed to delivering the safest, most reliable launch vehicles on the market today.  We appreciate SES’s early confidence in SpaceX and look forward to launching additional SES satellites in the years to come.”

The mission marked SpaceX’s first commercial launch from its central Florida launch pad and the first commercial flight from the Cape Canaveral Air Force Station in over four years.  SpaceX has nearly 50 launches on manifest, of which over 60% are for commercial customers.

This launch also marks the second of three certification flights needed to certify the Falcon 9 to fly missions for the U.S. Air Force under the Evolved Expendable Launch Vehicle (EELV) program. When Falcon 9 is certified, SpaceX will be eligible to compete for all National Security Space missions.

Clues to the SpaceX “Big Rocket”

NSS Board of Directors member John K. Strickland reports:

A major clue to the “Big Rocket” from SpaceX (bigger than the Falcon Heavy) was recently revealed when an agreement with the Stennis Space Center to test the Raptor engine showed that its vacuum thrust is almost 600,000 lbs. We had been expecting a much smaller engine for upper stage use. This means the methane oxygen engine could be used on both the first and second stages of the Big Rocket.

We could assume that the same configuration as the Falcon 9 is used, with the upper stage having a single engine with a nozzle extension to allow greater thrust in space, and with the engine-out capability of the 9 engine Falcon 9, duplicating its basic eight-and-one first stage configuration with the new engines. This would mean that the Big Rocket’s total thrust would be about 5.4 million lbs of thrust (about 2500 tons at sea level), more than 2/3 that of the Saturn V, and with more efficient engines to boot.

Methane engines have a higher specific impulse than the RP1 and oxygen used in the Merlins. The new engine will also use combined cycle or closed loop combustion, a significant improvement over the existing Merlin engine design. This means the engines can produce more thrust with the same amount of fuel, part of Musk’s deliberate process of “continuous improvement.”

One observer wondered if the rocket could use 11 such engines, 10 in a circle and one in the middle. This would depend on the width and spacing requirements of both the engines and the first stage circumference. With this configuration, the total thrust would be 6.6 million lbs.

This means that the Big Rocket is not just a publicity gambit, as some critics have alleged. The 27 foot diameter given for the Big Rocket now makes sense. Such a rocket could launch cargo or vehicles up to 40 feet in diameter in a reverse fairing.

An article in the Oct 28 edition of Space News says that parts for the Raptor methane-oxygen engine will be tested at Stennis early in 2014. This indicates that Raptor development is well under way. It is unclear how long it will take to build a new test stand for a 600,000 lb thrust engine, six times what current stands there can test.

The engine is described as “highly reusable.” One would then think that the HLV Big Rocket it is designed to work with would also be “highly reusable.” The SpaceX spokesperson said that it was the first in what would be a family of engines. Based on the known development times for the Falcon family, the Big Rocket should be ready to fly (and land for another flight) well before 2020.

It is unclear if such engines will be tested at any other locations, and also what the schedule might be for the actual rockets that would use them. A short, fat booster is structurally much easier to get down into the troposphere intact than a long skinny booster like the Falcon 9.


Experimental Spaceplane Shooting for “Aircraft-Like” Operations in Orbit

New program seeks to lower satellite launch costs by developing a reusable hypersonic unmanned vehicle with costs, operation and reliability similar to traditional aircraft

Commercial, civilian and military satellites provide crucial real-time information essential to providing strategic national security advantages to the United States. The current generation of satellite launch vehicles, however, is expensive to operate, often costing hundreds of millions of dollars per flight. Moreover, U.S. launch vehicles fly only a few times each year and normally require scheduling years in advance, making it extremely difficult to deploy satellites without lengthy pre-planning. Quick, affordable and routine access to space is increasingly critical for U.S. Defense Department operations.

To help address these challenges, DARPA has established the Experimental Spaceplane (XS-1) program. The program aims to develop a fully reusable unmanned vehicle that would provide aircraft-like access to space. The vehicle is envisioned to operate from a “clean pad” with a small ground crew and no need for expensive specialized infrastructure. This setup would enable routine daily operations and flights from a wide range of locations. XS-1 seeks to deploy small satellites faster and more affordably, while demonstrating technology for next-generation space and hypersonic flight for both government and commercial users.

“We want to build off of proven technologies to create a reliable, cost-effective space delivery system with one-day turnaround,” said Jess Sponable, DARPA program manager heading XS-1. “How it’s configured, how it gets up and how it gets back are pretty much all on the table—we’re looking for the most creative yet practical solutions possible.”

DARPA seeks ideas and technical proposals for how to best develop and implement the XS-1 program. The agency has scheduled an XS-1 Proposers’ Day for Monday, October 7, 2013. The agency also plans to hold 1-on-1 discussions with potential proposers on the following day, October 8, 2013. Advance registration is required; more information is available at Registration closes on Tuesday, October 1,2013, at 12:00 PM EDT. For more information, please email

The DARPA Special Notice describing the specific capabilities the program seeks is available at A Broad Agency Announcement (BAA) for XS-1 is forthcoming and will be posted on the Federal Business Opportunities website.

XS-1 envisions that a reusable first stage would fly to hypersonic speeds at a suborbital altitude.  At that point, one or more expendable upper stages would separate and deploy a satellite into Low Earth Orbit. The reusable hypersonic aircraft would then return to earth, land and be prepared for the next flight. Modular components, durable thermal protection systems and automatic launch, flight, and recovery systems should significantly reduce logistical needs, enabling rapid turnaround between flights.

Key XS-1 technical goals include flying 10 times in 10 days, achieving speeds of Mach 10+ at least once and launching a representative payload to orbit. The program also seeks to reduce the cost of access to space for small (3,000- to 5,000-pound) payloads by at least a factor of 10, to less than $5 million per flight.

XS-1 would complement a current DARPA program already researching satellite launch systems that aim to be faster, more convenient and more affordable: Airborne Launch Assist Space Access (ALASA). ALASA seeks to propel 100-pound satellites into orbit for less than $1 million per launch using low-cost, expendable upper stages launched from conventional aircraft.

“XS-1 aims to help break the cycle of launches happening farther and farther apart and costing more and more,” Sponable said. “It would also help further our progress toward practical hypersonic aircraft technologies and increase opportunities to test new satellite technologies as well.”

SpaceX Grasshopper Successfully Completes 100m Lateral Divert Test

On August 13th, the Falcon 9 test rig (code name Grasshopper) completed a divert test, flying to a 250m altitude with a 100m lateral maneuver before returning to the center of the pad. The test demonstrated the vehicle’s ability to perform more aggressive steering maneuvers than have been attempted in previous flights.

Grasshopper is taller than a ten story building, which makes the control problem particularly challenging. Diverts like this are an important part of the trajectory in order to land the rocket precisely back at the launch site after reentering from space at hypersonic velocity.

Boeing Unveils CST-100 Spacecraft Interior

And Space Adventures plans to sell flights on the CST-100, having recently signed a contract with Boeing to that effect. No word yet on cost and availability.

Article below by Rebecca Regan, NASA Kennedy Space Center

Two NASA astronauts conducted flight suit evaluations inside a fully outfitted test version of The Boeing Company’s CST-100 spacecraft July 22, the first time the world got a glimpse of the crew capsule’s interior.

“The astronauts always enjoy getting out and looking at the vehicles and sharing their experiences with these commercial providers,” said Kathy Lueders, deputy manager of NASA’s Commercial Crew Program (CCP).

Boeing is one of three American companies working with CCP to develop safe, reliable and cost-effective crew transportation systems during NASA’s Commercial Crew Integrated Capability (CCiCap) initiative, which is intended to make commercial human spaceflight services available for government and commercial customers.

During two, four-hour sessions, astronauts Serena Aunon and Randy Bresnik put on NASA’s iconic orange launch-and-entry suits and then individually tested their maneuverability inside the capsule. Meanwhile, Boeing engineers monitored communications, equipment and ergonomics.

“These are our customers. They’re the ones who will take our spacecraft into flight, and if we’re not building it the way they want it we’re doing something wrong,” said Chris Ferguson, director of Boeing’s Crew and Mission Operations and a former NASA astronaut. “We’ll probably make one more go-around and make sure that everything is just the way they like it.”

The CST-100 test vehicle was optimized to seat five crew members, but the spacecraft could accommodate up to seven or a mix of crew and cargo. While the spacecraft may resemble Boeing’s heritage Apollo-era capsules from an exterior perspective, its interior is a reflection of modern technology. From the ambient sky blue LED lighting and tablet technology, the company ensured the CST-100 is a modern spacecraft.

“What you’re not going to find is 1,100 or 1,600 switches,” said Ferguson. “When these guys go up in this, they’re primary mission is not to fly this spacecraft, they’re primary mission is to go to the space station for six months. So we don’t want to burden them with an inordinate amount of training to fly this vehicle. We want it to be intuitive.”

Other innovative element of the CST-100 is its weld-free design, modern structures and upgraded thermal protection techniques. The company said its spun-formed shell reduces the overall mass of the spacecraft as well as the time it takes to build the crew capsule. “I’m really a looking forward to the day when we will be bringing our Expedition crew members home and I won’t need a passport or a visa to go to the landing site and greet them as they come off the vehicle,” Lueders said.

Paths to Space Settlement

The latest paper in the NSS Journal of Space Settlement is “Paths to Space Settlement” by Al Globus.


A number of firms are developing commercial sub-orbital launch vehicles to carry tourists into space. Let’s assume they attract many customers and become profitable. The next, much more difficult, step is to develop orbital tourist vehicles and space hotels to go with them. These hotels will require maids, cooks, waiters, concierges and so forth, some of whom may decide to stay, becoming the first permanent residents in space. A luxury hotel plus good medical facilities could provide low-g living for wealthy disabled individuals where wheelchairs and walkers are unnecessary.

In the meantime, humanity could choose to solve, once and for all, our energy and global warming problems by developing space solar power. To supply a substantial fraction of civilization’s 15 TW energy consumption would require an extremely large number of launches, the ability to build extremely large structures in orbit, and eventually tapping the Moon and Near Earth Objects (NEOs) for materials to avoid the environmental cost of mining, manufacturing, and launch from Earth.

The first step towards NEO mining is to locate them. As a large fraction, roughly 30%, of these will eventually impact Earth, locating and characterizing the NEO population is essential for planetary defense. Furthermore, it would be prudent to deflect a representative set of non-dangerous NEOs to insure that we know how to do it should a NEO on an imminent collision course with Earth be found. A representative set would include at least one of each major type of NEO since these have different physical properties and thus may require different deflection techniques. This would give orbital space settlement designers a known source of materials and the means to move them if necessary.

If these paths are taken, each step of which is justified in its own right, humanity will have excellent launch, small orbital living facilities, the ability to build large objects in orbit, and access to extra-terrestrial materials — most of what is needed to realize Gerard O’Neill’s orbital space settlement vision. At that point, some extremely wealthy individuals may build themselves a small orbital habitat so they live only with like-minded individuals. The first, and most difficult, orbital space settlement will be built.

These are paths to space settlement.

Full paper.