Today, we discuss the first, and most important, space vehicle needed to build upon that solid foundation, and achieve that sustainability (Click here for the list of topics for this series).
Spaceflight operations should be a relatively simple and routine affair in the 21st century, just like what we saw in the movie 2001: A Space Odyssey, where the Pan Am shuttle is rendezvousing with the space station.
Therefore, the spacecraft should have the following characteristics:
While the three spacecraft that were awarded money from NASA under the Commercial Orbit Transportation Services (COTS) contract can achieve some of the items on the list, all three cannot be launched from Spaceport America, since they all use expendable rockets to achieve orbital velocity.
- Single Stage To Orbit (SSTO) capability
- Totally reusable, i.e., non-expendable
- Self-Ferrying capability
- Remotely Piloted (while in cargo mode)
- Minimum orbital altitude of 185 km (115 mi)
- Orbital inclination of 33 degrees (Spaceport America Latitude)
- Cylindrical payload bay dimensions of 4.57 m (15 ft) diameter by 12.19 m (40 ft) length
- Maximum payload mass of 14,742 kg (32,500 lbs)
- Ability to carry into Low Earth Orbit (LEO) either cargo or a Passenger Module capable of carrying 20 passengers plus the pilot
- Each passenger seat must come with its own pressure suit, a Cargo Transfer Bag (CTB), and a 4 day supply of O2/Lithium Hydroxide
- Including the weight of the passenger, each seat must weigh no more than 195 kg (430 lbs)
- Ability of the Passenger Module to withstand a crash landing
- Ability of the Passenger Module to parachute to a (relatively) soft landing if ever thrown clear from a disintegrating shuttle
- Flight endurance of 48 hours (nominal) and up to 96 hours during emergencies
- A turn-around time of one week between flights
- Total spacecraft lifetime of 200 flights
But even if they could be launched from the Spaceport, the Space X Dragon has a payload capacity of only 6,000 kg (13,228 lbs) or a crew of 7. The same is true for Sierra Nevada's Dream Chaser, as well as Boeing's CST-100. In addition, the turnaround time is much greater than one week for each of the three spacecraft.
We tried very hard to fit our plan around the launch capabilities of the NASA three, but were unable to do so in an operationally efficient and cost-effective way. We were very disappointed. We then faced either a) giving up, or b) designing and building our own shuttle with the aforementioned capabilities. We dismissed option a) without a second thought, and understood that option b) was unrealistic, as it would add an enormous cost to an already expensive adventure.
Therefore, we came to the depressing conclusion that there are currently no spacecraft flying or still in the design phase that can even come close to achieving everything on the list above.
Well, OK. Except for one.
While all this fierce competition for the NASA dollar was going on in the US, on the other side of the Atlantic something very interesting was quietly developing.
A company called Reaction Engines, located at the Culham Science Centre in Abingdon, Oxfordshire, Great Britain, was in the process of building a Horizontal Takeoff/Horizontal Landing (HTHL) space plane called the Skylon. The Dragon, in contrast, is a Two Stage To Orbit (TSTO), Vertical Takeoff/Vertical Landing (VTVL) spacecraft, using expendable launch vehicles to get to orbit.
The Skylon is a true SSTO, HTHL, fully reusable spacecraft, that takes off and lands and operates like an ordinary jet airliner.
The spacecraft is still in the design phase, but the research looks very promising.
They have designed a hybrid engine called SABRE (Synergetic Air-Breathing Rocket Engine) that burns Liquid Hydrogen (LH2) fuel, and uses atmospheric oxygen as the oxidizer during the first part of the ascent into space. Liquid Oxygen (LO2) is used in the second part of its flight. Liquid Helium (LHe) is used as a heat sink to cool incoming air during the first phase of the flight, and to push the propellant out of their tanks during the second phase.
The SABRE recently completed a major milestone, where they successfully tested a prototype of the heat exchanger needed to cool the atmospheric oxygen to minus 150 degrees C in an astonishing 1/100th of a second!
A problem did arise during the early days of development that was solved with a little ingenuity, IMHO. The brakes needed to slow the spacecraft to a halt should a takeoff abort be necessary were not adequate, at least not without raising the empty weight to an intolerable amount with beefed-up brakes. So they designed a brake cooling system using 3,000 kg (6,614 lbs) of water that would be applied during an emergency. Once the Skylon becomes airborne, the water is dumped overboard to save weight. Genius! We would like to supplement this brilliant idea by developing a way to reclaim the dumped water for recycling.
Flight Testing and Delivery
These two topics are under one roof because they both use the same technique for each scenario.
All the spacecraft that come out of the factory will have to be flight tested. To accomplish this, the spacecraft would be filled with LH2 fuel and flown in self-ferrying mode using atmospheric O2 as the oxidizer. Eventually, flight tests will progress to orbital operations.
Delivery to the Spaceport would be accomplished using orbital flight. The Skylon would be filled with propellant at the factory, then fly into LEO for a final flight test. The Skylon then reenters and lands at (is delivered to) the Spaceport.
The spacecraft is remotely operated while flying cargo. The remote pilot flies the Skylon from Mission Control at the Spaceport, with the Flight Director and the other flight controllers surrounding the pilot.
The pilot operates a standard remote flight deck that resembles a flight simulator. The pilot would have a large screen to view, with an accompanying camera aboard the Skylon. Aircraft and spacecraft instruments would surround the remote pilot, again, as if in a flight simulator. The pilot would fly using a standard stick-and-rudder system, with throttles on the left-side console.
All Skylons will therefore have an "Access Code," similar to what we saw in the movie "Star Trek II: The Wrath of Kahn." Each Access Code would be valid for the duration of the mission only (this part of the plan is not without some inherent danger of being hacked, so, obviously, due vigilance is called for).
Passenger Module The Skylon people have developed their own Passenger Module (PM). It can hold 24 seats, plus 700kg (1,543 lbs) of CTBs.
I do not have evidence for this, but IMHO, I do not believe that passengers will be willing to fly in space and back aboard a ship without a pilot onboard. Therefore, when in passenger mode, we would modify things slightly by making the remote pilot the copilot while the pilot flies the spacecraft remotely from inside the spacecraft.
A duplicate of the system in Mission Control will be flown aboard the spacecraft, which we hope weighs at the maximum the equivalent of three (3) passengers seats, or about 585 kg (1,290 lbs). There is no need for a physical control connection to the Skylon PM itself, since it already receiving a clear signal (this is analogous to having a wireless system next to your computer verses down the hall). Including the pilot, this now reduces the number of passenger seats to 20 for the same amount of weight.
A very nice safety feature thus arises, whereas any spacecraft can be flown from the ground by the copilot should the pilot onboard ever become incapacitated, or should the onboard systems ever fail, or should _________________ (insert horrible scenario here).
Other safety features include the PM using the empty fuel tanks as "crumple zones" to survive a crash landing, the ability of the PM to survive an explosion during liftoff, the ability of the PM to parachute to a safe landing if ever thrown clear of an exploding spacecraft, etc. Overall, the passengers and crew are as safe as can be.
The PM is loaded into the Skylon spacecraft as any other payload; the Payload Integration Facility lowers the PM into the payload bay, and the payload bays doors close. Passengers enter the spacecraft through the hatch shown in the lower right of the image above. They then enter the Passenger Module inside the payload bay, while the payload bay doors remain closed.
Cargo capacity for a given orbital altitude from a latitude of 33 degrees into a 33 degree inclination LEO can be modeled by the linear function:
m(a) = -8.2a + 16,336
where a = altitude (in km) and m = payload mass (in kg)
To determine the orbital altitude for a given payload mass, solve the function for altitude.
a(m) = (m - 16,336) / (-8.2)Therefore, a fully-loaded Skylon space craft (payload mass of 14,742 kg or 32,500 lbs) can reach an orbital altitude of 194 km (121 mi). The PM (mass of 13,180 kg or 29,057 lbs) can reach an orbital altitude of 385 km (239 mi).
A Typical Flight
A typical flight begins in the Payload Integration Facility, where an overhead crane lowers the payload into the Skylon payload bay and is secured for flight. The payload bay doors then close, and an airport ground vehicle backs up and hooks up to the nose of the spacecraft.
The spacecraft is then towed to the propellant apron, where LH2, LO2, and LHe is pumped in through the landing gear area of the spacecraft. Total propellant weight is 277,000 kg (610,681 lbs).
Once the fuel has been loaded, the Skylon spacecraft is then towed to the runway for immediate takeoff, just like any other ordinary airliner. No expensive launch towers needed! Gross takeoff weight is 345,000 kg (760,595 lbs). For comparison, gross takeoff weight for a 747-8 is 448,000 kg (987,000 lbs).
Once the Skylon breaks ground, the coolant water is dumped overboard, and the spacecraft continues to climb out, gaining altitude and speed.
Then, at 5.14 Mach and 28.5 km (17.7 mi) altitude, the fun begins. What was once the feverish secret fantasy of all aerospace engineers is now fully realized: the spacecraft turns off its air-breathing component and switches to the onboard LO2 to blast its way into LEO!
The spacecraft engines continue to burn until Main Engine Cut Off (MECO) at an altitude of 80 km (50 mi). The Skylon then coasts up to the desired orbital altitude. A kick motor (an RL-10 rocket) in the tail of the spacecraft provides the delta v needed to circularize its orbit. The spacecraft flight profile then mirrors the US Space Shuttle from this point on.
Once in LEO, the payload bay doors open, revealing the cargo. Once the cargo is unload, other cargo is loaded for the return trip to the Spaceport.
Alternately, if the PM is flown, then the Skylon can dock directly with the (future) space station. There, 20 passengers and 700kg of CTBs are offloaded, then another 20 passengers and another 700 kg of CTBs are on-loaded. The Skylon then undocks, and moves away to a safe distance. The payload bay doors close, and the tail kick motor fires again to lower its perigee into the atmosphere for reentry.
During reentry, the spacecraft performs S-Turns and other power management maneuvers. Minimum landing weight is around 53,000 kg (116,845 lbs), and a maximum landing weight of 67,742 kg (149,346 lbs). Landing speed is 130 knots (151 mph) with crosswinds of up to 30 knots (35 mph).
If the Skylon needs to make an emergency landing, any airport with a reinforced concrete runway will do. Once the spacecraft lands, a standard ground vehicle will hook up, and tow it off the active runway. A C-17 will be dispatched, with a cargo hold full of LH2. The Skylon is refueled, and self-ferrys back to the Spaceport. If the Skylon needs more than one hop to get home, the C-17 meets the spacecraft at whatever airport the spacecraft can reach. The steps are repeated as necessary.
After it rolls to a stop at the Spaceport, the Skylon is then towed back to the Payload Integration Facility. Skylon publishes a turnaround time of two (2) days, but we will play it safe and assume a seven (7) day turnaround (still very impressive by US Space Shuttle standards). The spacecraft is then refurbished, reloaded, refueled, and returned to space.
The whole thing will be run just like any ordinary airline!
A stable, consistent flight schedule can now be created. We envision two (2) flights per day, five (5) days per week (Monday through Friday), or ten (10) flights per week. Mission duration, ie, the time between takeoff and landing will be 48 hours. The 2 flights a day can have any amount of time between launches; however, if launches occur every 12 hours, then landing and takeoff ops will be occurring at the same time. So the time interval between the two daily launches needs to be less than 12 hours per day.
Assuming 50 flight-weeks per year, that comes to 500 flights every year, for the next ten years. Two (2) of the weekly flights will be passenger flights, while the other eight (8) will be cargo flights. We will therefore be able to lift a total of 117,935 kg (260,000 lbs) and 40 passengers into LEO every week!
Granted, all that cargo seems to be 8 separate 4.57 m by 12.19 m (15 ft by 40 ft) pieces, but if we design things right (which, of course, we will), those pieces should fit together like the proverbial well-made jigsaw puzzle (but that's for a future diary!).
We are assuming, until otherwise confirmed, a unit cost of around $750M USD per spacecraft, or a little over twice the cost of a 747-8 per unit. A fleet of 12 shuttles was also assumed, where 10 fly at any given time while 2 are down for preventative maintenance. The fleet is then rotated so that each spacecraft gets their routine, scheduled maintenance. Total cost for the shuttle fleet: around $9B USD.
Using the estimated cost of $2B USD for Spaceport America upgrades, the total so far for our space program is around $11B USD.
Skylon User's Manual: (PDF) http://www.reactionengines.co.uk/tech_docs/SKYLON_User_Manual_rev1-1.pdf
Note: The next article in this series involves the LEO infrastructure, and some of the details still need to be worked out. Posting may be delayed as a result. Stay tuned!