What Space Tourism Needs

Cropped A3 Poster with Red Button

Want to get into space? Heck – who doesn’t!

In the early days of space exploration the vehicles were the equivalent of experimental coupes with no room in the back. Rockets like the Saturn V had a lot of power under the hood, but the capsule had no seats for the kids or friends.

Kudos to Virgin Galactic for taking the next step, with vehicles for up to six passengers. These lucky six will be paying anywhere from US$95,000 to US$250,000 depending on the length of the journey. This upgrades us from two-seater to an Orbital Minivan, but really this is still only an extreme sport for the super wealthy. Maybe not the spouse in the passenger seat and kids in the back — more like the CEO and his lucky executives.

True space tourism would be closer to the model we have today with commercial aviation, opening up the unique travel and leisure opportunities for a wider population. That would require something akin to a tourist bus.

Interestingly, the designers of the Space Shuttle originally intended it to be used as far more than a cargo carrier, with some designs carrying up to 74 passengers in a modified rear compartment or ‘passenger module’. Check out the graphic below (attribution: chron.com blog).

the_future_of_space_tourism_6 - chrondotcom blog

Even more fascinating is the fact that the Shuttle was also originally conceived with a reusable manned booster. The problem was the manned booster was about the size of an aircraft carrier. Yet if they had managed to build it, the overall cost of spaceflight might have dropped substantially, taking advantage of the fact that the fuel is only about 1% of the cost of getting into orbit.

It is interesting to note that the development of reusable boosters (unmanned), is the key focus of Space X for this exact reason (i.e. that the hardware is where the real cost is, not the fuel).

If only. . .



Reusable Rockets One Step Closer

Hey, did I mentioned the three books in my Jakirian Cycle are out:)

New Calvanni CoverScytheman CoverSorcerer Cover


For a while now Elon Musk’s Space X has be busily working away at developing a reusable rocket system, with both a first and second stage that can be reused with hours of return.

The Grasshopper rocket is the test vehicle for the reusable first stage. Earlier in the year this reached a height of 325m and then touched down again. In its latest test flight on October 7,  the Grasshopper reached a height of 744m and landed right back down on the launch pad. It’s an awesome thing to see. Check out the footage, which was captured by a remote controlled hexacopter stationed in the sky. The rocket lands on a dime. Amazing control.

Hey, Elon Musk, can I come work for you? I’m a real engineer, honest.

OK. Back to reality.

The plans are to continue to extend the height at which the Grasshopper stops and returns to the launch pad.

In the meantime, Space X has progressed the other part of the proposed testing regime by performing the first test on a returning Falcon 9 first stage booster. The Falcon 9’s engines were re-lit twice on the way down during the September 29 test flight from Vandenberg Air Force Base in California. The two burns eased the vehicle’s return to Earth, where it eventually splashed down over the Pacific Ocean.

The Falcon 9 v1.1 carried Canada’s CASSIOPE space-weather satellite and three smaller spacecraft to orbit. As its first stage fell back to Earth, the secondary test program was initiated.

The first burn ( where three engines were ignited for supersonic retro propulsion) enabled the returning first stage to survive atmospheric re-entry without burning up. The second burn (with a single engine) went well, although the splashdown was a little harder than planned due to a roll developed by the returning vehicle.

Exciting stuff, and right in line with Space X’s stated development path. The company now believe they have ‘. . . all the pieces to achieve a full recovery of the boost stage.’

One step closer to a true reusable rocket and a system with will get us ‘up there’ at last:)

200 Year Old Technology Makes it into Space – The Stirling Radioisotope Generator

For those of you who have not heard about the Stirling engine, the technology was first proposed by Scotsman Robert Stirling way back in 1816 as an alternative to nasty steam engines, which had a habit of exploding and killing people with high-pressure steam. In nineteenth century steam engines, water inside the pressure vessel was in two phases – steam vapour and pressurised liquid, so in the case of a rupture there was an instant expansion of hot liquid into steam.

Often called an ‘external combustion engine’, Stirling engines are a sealed system with the cylinders inside working with a gas, such as air or nitrogen, which exists in a single phase.

The physical layout of the Stirling engines varies, but all have a ‘power’ piston and a ‘displacer’ that works in concert with the power piston to maintain the constant volume conditions. Each engine has a hot and cold end, with a heat exchanger at each. Inside the engine is a ‘regenerator’,  which is a physical material that stores part of the heat as it flows inside the engine and is crucial to its operation.

Stirling engines have been demonstrated at temperatures well below 100oC. The Ultra Low Temperature Difference Stirling engine was demonstrated to operate at a hot side temperature of just 0.5oC. Like any heat cycle, it is driven by temperature difference, so a low hot side temperature must be balanced by an even lower cold side where heat can be rejected. In practice low temperature differential Stirling engines require a very large surface area for heat transfer and are consequently more expensive to manufacture than high temperature Stirling engines.

The real advantage of Stirling engines lies in their heat source flexibility. The same Stirling engine can operate with a wide range of fuels and over a wide range of temperatures.

NASA have been working for some time on a small Stirling engine for use as a power supply on spacecraft. Called the Advanced Stirling Radioisotope Generator (ASRG), it is driven by the heat from radioactive decay.

Around 1kg of Plutonium 238 forms part of the module. This generates a thermal output of around 500 Watts. The heat drives a small, single cylinder Stirling engine that produces around 140 Watts of electrical power.

Like all Stirling engines, the ASRG is a closed-loop engine. It’s internal working gas will be helium. In its single cylinder the up-down motion of the power stroke is converted into an AC electrical output by a linear alternator. This is then converted to the DC required by on-board systems.

Why would NASA bother putting something with that many moving parts on a spacecraft? Well for a start, Stirling engines are very reliable, and a large part of the work the NASA is undertaking is focussed on reliability studies for the ASRG. But primarily, the ASRG will be four times more efficient per unit mass than the Radioisotope Thermoelectric Generator (RTG) it replaces. That is an impressive increase in efficiency. The RTG modules have been standard on spacecraft for the last 40 years, and use the temperature differential in thermocouples to produce power.

To reduce vibration, two ASRG  units will be mounted opposite each other and synchronised so their pistons move in opposite directions to eliminate mechanical noise.

An RTG system has a typical efficiency of around 5-7%, disappointingly low considering it is driven by 850oC from the Plutonium power source. The ASRG’s Stirling generator would operate at around 38% efficiency with the same 850oC hot end (with heat rejected the lonely depths of space at 90oC). In practice the ASRG’s hot end temperature, and consequently, net efficiency is expected to be a little lower.

The ASRG was demonstrated for the first time in 2012 – the first demonstration of a new nuclear system for power production since 1965. There are also moves to produce more Plutonium, again for the first time since 1965.

The ASRG could be available as early as 2015, and is designed to have a 14 year mission life.

Larger versions have been proposed to power a potential Moon base, and also a Mars base under the NASA Fission Surface Power project. So far a 40kWe version has been trialled in NASA labs (minus the nuclear fuel source i.e. just the Stirling engine component with conventional heat applied). This 40kWe version is likely to be the size of a trash can, and would provide surface power for decades with little or no maintenance.

Around 40 kWe is about the size of generator you need to power a small hybrid-electric vehicle. Maybe NASA would consider selling Plutonium cars to the public? It would be cool to drive around for a couple of decades and never fill up. When you are not driving you could plug it into your house and power both you and your neighbours.

Hey, it’s nice to dream:)

Space X Grasshopper Reusable Rocket

If you’ve been reading this blog for a while, you probably heard me talking about Elon Musk’s Space X and the plans to develop a reusable rocket system. The theory is that it’s the cost of space craft that overwhelmingly contributes to the high cost of getting into orbit. The fuel itself represents perhaps 1% of the total cost. So if you can develop a truly reusable rocket system you can potentially revolutionise space travel. There are a few parts wishful thinking in this, and a few parts hyperbole, but it’s an intriguing concept nonetheless. Meanwhile, Space X is forging ahead.

Space X have been developing a reusable system based on their Falcon 9 launch vehicle platform. This launch vehicle is a pretty familiar sort of beast – a two stage rocket powered by liquid oxygen and kerosene. It has established a solid performance record to date and was used by Space X for a visit to the International Space Station, the first by a commercial company.

The Space X Grasshopper is designed to take the place of the Falcon 9’s first stage. It has been in active testing since September last year. So far it has had six test flights, each gradually extending the height at which the rocket stops, hovers then touches back down. Both take off and landing are vertical (VTVL). The latest (check here for video) took the venerable Grasshopper to 325m (1066 feet), with an overall duration of 68 seconds. It’s likely the tests will extend substantially, perhaps reaching altitudes of up to 91 kilometres (57 mi) with the second generation of the test craft.

If you want a bit of entertainment, check out this video of one of the early tests that plays to Jonny Cash’s ‘Ring of Fire’. LOL.

The second generation of Grasshopper will have lighter-weight landing legs that actually fold up into the rocket. I can’t help but be reminded of those sleek 1950s art-deco SF rockets than come down to land on their legs in such a similar manner, except they (of course) had three legs whereas Grasshopper has four. The Grasshopper’s legs use a telescoping piston on an A-frame, actuated by high-pressure helium.

Plans are to start testing the decent of Falcon 9 first stages to confirm the technology. Each first stage of the Falcon 9 will be equipped and instrumented as a controlled descent test vehicle. They will initially do the propulsive return tests over water until they can complete a return to the launch site with a powered landing, perhaps as early as 2014.

Ultimately the first stage separation will occur at around Mach 6, rather than the current Mach 10 for the expendable version of the Falcon 9. This is to ensure there is sufficient fuel for deceleration, controlled descent and landing.

I have a feeling that once this system is up and running, expendable launch systems will seem like the crazy idea, not reusable ones!

But the Grasshopper, as impressive as it is, is only half the launch system. The first stage will separate and be back on the launch pad minutes after the launch. The reusable second stage will take up to 24 hours to return to the launch pad, to allow for orbital realignment and atmospheric re-entry. Both stages are envisaged to be available for reuse within hours of return.

Eventually the reusable launch system technology will be applied to both the Space X Falcon 9 and Space X Falcon Heavy launch vehicles.

I think we are watching history in the making.

The Return of Air-Breathing Engines

I was reading recently about the Skylon space plane. A pretty cool name, which reminds me of those robotic guys with the light bouncing back and forward where their eyes should be  – the vintage Cylons of Battlestar Galactica.

The Skylon spaceplane is a concept for a Single Stage to Orbit (SSTO) plane, which has been a holy grail for the aerospace industry for many decades.

Although the theory of payload Vs rocket mass takes concepts in the direction of multi-staging and non-renewable spacecraft – such as the good old Saturn V and modern equivalent the SpaceX Falcon 9 – the ability to reuse the same spacecraft also makes good economic sense. All rocketry components are damn expensive. Besides it’s such a damn cool idea to be able to get into a spaceplane at the local airport, taxi down the runway and blast into orbit.

What may make this particular SSTO dream feasible is the return of the air-breathing engine. Some of you might remember the HOTOL concept from the 1980s.  The moniker stood for Horizontal TakeOff and Landing. I remember being really excited about this joint venture between Rolls Royce and British Aerospace, but apparently funding was cut in 1988 due to serious design flaws and lack of advantage over contemporary launch systems.

Like HOTOL, Skylon features air-breathing engines that use oxygen in the atmosphere as the fuel oxidant [it later switches to liquid oxygen in space]. The majority of fuel tankage is reserved for hydrogen, removing one heck of lot of weight compared to say a shuttle with its big external tank of hydrogen and oxygen. One key feature of the Skylon’s SABRE engines is the cooling of the intake air, which enables a doubling of the efficiency.

The estimated top speed of Skylon is over 30,000 km/h. This gives the craft plenty of scope to fill the niche left by the ill-fated Concorde, with sub-orbital flight times of around 4 hours from London to Sydney. Having suffered through two 30 hour flights to the USA in economy I can’t wait.

The initial goal is to carry payloads to space stations by 2022. English developer Reaction Engines hope to have a working prototype flying by 2016, and a fleet of the craft over the next decade. They are impressive craft. Each will be approximately 82 metres in length with a price tag of around $1.1 billion US.

The spaceplane is a very sleek looking craft. Check out the wikipedia page for graphics.