ThunderStruck Spacecraft – a First for Australia
Yes, Australia has built vehicles that have gone into space, but ThunderStruck will not be an orbiting satellite. It will be a vehicle that has propulsion other than that used for orbital watch-keeping. It is being designed to have both an Ion Engine for long distance travel and also a high DeltaV for rendezvous and reentry control.
So what is DeltaV?
Simply: Delta-V, or dV as it’s sometimes abbreviated, is a measure of the total amount of acceleration (or deceleration) your ship can output. Skip down to the next heading if you hate maths!
Mathematically, delta-V takes the form: delta-V = ln(M/Mo)* Isp *go
where delta-V is the change in velocity, ln is the natural logarithm function (look for it on a scientific calculator, or use =LN() in MS Excel), M is the full mass of the rocket stage, Mo is the dry mass of the rocket stage (i.e. what it weighs when all its fuel tanks are empty), go is standard gravity (9.81 m/s2 regardless of what body you’re orbiting/launching from) and Isp is the specific impulse of the engine (a way of measuring the engine’s efficiency). It’s importance, is in determining the total magnitude of the changes the rocket may make to its velocity before it runs out of fuel; in the process it determines where a rocket may go given a certain mission profile. There are three main ways of increasing a rocket’s delta-V:
1) improving propellant mass fraction (i.e. more fuel)
2) increasing specific impulse (by selecting an engine combination that increases this value
3) staging (shedding mass that’s no longer needed, which has the effect of improving the propellant mass fraction)
With an Ion engine, we expect it to be huge, but this spacecraft is designed to re-enter Earth’s atmosphere and land, so we have to slow and return. Basically, however long we took to get there, will also be how long it takes to slow. We will have some ways of beating that equation, but for now, we have to understand that Ion engines have an appallingly low DeltaV. That is why we need strong thrusters for the craft and a radically different system to make the craft more versatile. None the less, ThunderStruck is being built for orbit but also for round trips to the Moon, Mars and Asteroids. With an upper design payload of around 50Kg, it should be able to handle significant experiments. The most appealing destination for long flights is of course the asteroid belt. ThunderStruck’s main role as a space taxi will be to meet with survey vessels to bring back payloads. The survey vessel will need to be able to rendezvous with ThunderStruck, remove the empty container and load the full container for the trip back to earth.
ThunderStruck is a Space Taxi – but not for people
Most craft are built uniquely for every mission. ThunderStruck is a “space taxi” built to a standard design. it will have a payload that will be able to be opened to space for any science such as collecting particles or other experimentation and be closed again for the return to earth. It is envisaged that a capsule version will be available for high velocity returns to earth and it will use a parachute to land. A further version may be used in a one way trip and not need an ablative shield. This will make it inexpensive to get somewhere and the navigation can be handled by the ThunderStruck team’s mission control.
ThunderStruck and Cruise Mode
I mentioned that there was a way to save time and fuel. Simply that is to launch directly to the direction required by buying a ride on a launch vehicle with a bit of power. The rocket can power us to fly in the right direction with plenty of speed. This either lowers the fuel consumption or the time taken, or a bit of both. None the less getting to your destination with more fuel and in less time is a good start to the flight. Launches like this are not precise. We will spend some time and fuel correcting the trajectory , and with an ion engine, that can take time. None the less in Cruise mode, we will put the bulk of the craft to sleep for periods. This lessens the load on the electronics and can provide more of our solar power to the payload that may in fact be fully operational. In Cruise mode all unnecessary systems will be shut down. They may be woken up for checks on position and direction or orientation to the sun for the solar panels, etc. For such a long flight we will need to use systems like reaction wheels for orientation to ensure that fuel is not used. Solar is renewable. Thunderstruck will need both solar panels for the ion engines and solar power for the spacecraft systems. The ion engine will have its own solar units and Thunderstruck will deploy its own for the flight. these may vary depending on the payload requirements.
About halfway on a flight that has not had boost assistance, we need to turn the spacecraft around and fire the ion engines again to slow the craft. Using the ion engines, this will be the same time taken to accelerate to that speed. It is a slow braking system, but it must be done. If we are using a winged vehicle that is designed for re-entry for Low Earth Orbit (LEO), then we must slow to reach those speed and enter an orbit that will be suitable for a LEO re-entry. If we hit the atmosphere too hard, we could bounce off (like skimming stones on water) and our heat shield and structural integrity would both fail resulting in a breakup of the craft. As stated before a capsule version of the craft may allow us to re-enter at high speeds.
A First For Australia?
Well in fact a first for the entire world. There is nothing to currently service this part of the marketplace. The same winged craft without a massive heat shield could also do significant experiments using a sounding rocket – straight up to over 100Km altitude and back down for a landing.
Heating is insignificant compared to the fiery re-entry that we are accustomed to for orbital re-entry but still a concern that will be addressed. Cold gas thrusters will be all that is needed for flight control until the atmosphere thickens and also a feathering system to keep the spped as slow as possible.
Phase Two Testing from Space
This will occur in about 2 years time and will test the feathering system for a sounding rocket. If nothing else it is likely to be the commencement of building a return vehicle for sounding rocket flights as these can be serviced with different guidance systems and cold gas thrusters – very different from the ThunderStruck spacecraft.
The cold gas thrusters may only be needed before and after the period of “weightlessness” has been used for the experiment. Unlike the tourism spacecraft, sounding rockets are capable of flight higher than 105km and thus a reliable return craft would be a commercial success. It may still have the same shape of the ThunderStruck spacecraft, but have no need for space systems as we know them. It will still break the wound barrier, but be able to land near to the takeoff point. This means full video from space and the entire return flight and that of the payload.
Support for ThunderStruck
The world needs a craft of this capability and Australia needs a healthy space industry. please support ThunderStruck by:
- Linking to http://ptojctthunderstruck.org
- helping with fundraising
- contributing funds
- talking about ThunderStruck
- becoming a shareholder in the new company to own the intellectual property.
- Donate time and resources to assist the project.