Original URL: http://www.theregister.co.uk/2012/08/31/lohan_update/
LOHAN rolls out racy rocketry round-up
Progress to date on our audacious spaceplane mission
In response to requests from several Reg readers who've been following the progress of our Low Orbit Helium Assisted Navigator (LOHAN) ballocket mission, we've put together a round-up of just where we're at with the various aspects of the project.
The LOHAN team is fighting on several fronts to advance towards an explosive spaceplane climax, with the invaluable support of several companies who've chipped in kit, as well as volunteers who've stepped into the breach with expert assistance.
As is only right and proper, we'd also like to give a heads-up to all those readers who've offered quality advice and suggestions as we've battled away over the last year.
Here's our outline mission summary (click for a bigger version)...
...and the current lines of attack are:
- Vulture 2 spaceplane
- Rocket motor testing in the Rocketry Experimental High Altitude Barosimulator (REHAB) chamber
- Rocket motor heater
- Fantastical flying truss
- Mission electronics
1: Vulture 2 spaceplane
Our elite Southampton University team has been beavering away on the design of the spaceplane, which has presented some major technical challenges.
The aircraft is effectively required to act as both rocket and glider, meaning the team has to plan for two distinct flight phases: the launch from the flying truss and subsequent glide back to base under autopilot control.
As you can imagine, simply the calculations as to the centre of gravity shift as the rocket more burns its solid fuel reload have kept the chaps off the streets for a while.
They do, though, now have a working CAD model into which they can enter the parameters, and use to simulate the flight characteristics. Once they're satisfied, they'll fine-tune the CAD design for delivery to 3T RPD Ltd, who'll then ensure it's entirely ready for the 3D printing process.
Here's our video of Southampton's own printed aircraft - "Sulsa" - and the selective laser sintering (SLS) process, which shows just how the Vulture 2 will be hewn from the living nylon:
The design of the Vulture 2 is highly classified, so you'll just have to wait for the roll-out to admire its shapely form.
2: Rocket motor testing in the Rocketry Experimental High Altitude Barosimulator (REHAB) chamber
It's fair to say that the small matter of how to get a solid rocket motor to fire at altitude has been a right palaver. It's taken months to go from an initial concept of a shed-built hypobaric test chamber to the full-fat REHAB rig:
The bits and pieces are:
- Perspex lid
- Igniter cable
- REHAB chamber
- Vacuum pump
- Pressure gauge
- Digital thermometer
- Evacuation tube
- Thermocouple cable
- Safety tether tied to SPB standard brick
- Vacuum filter
- Insulated box
- Silicone seal
The only novelty here is the vacuum filter, which we've added to the system to allow us to see if the firing of reader Rob Eastwood's custom igniter is causing a significant pressure rise in the chamber prior to motor ignition.
The filter will intercept any smoke particles and other gunk from the igniter before it gets to the vacuum gauge - an expensive piece of kit kindly supplied by Applied Vacuum Engineering.
This means we can test for igniter-induced pressure rise without shutting off the isolation valve between chamber and gauge.
We'll give that a go next week. In the meantime, we do know that we can persuade a Cesaroni rocket motor to fire at around 20mbar - equivalent to 76,500ft (23,300m):
We've got more REHAB tests planned just as soon as a new batch of motor reloads turns up, so there's further low-pressure tomfoolery on the horizon.
3: Rocket motor heater
One big concern is the effect of cold on the rocket motor at altitude, where the temperatures can get down to -60°C.
After a few sleepless nights imagining a frozen cylinder of ammonium perchlorate composite propellant (APCP), we decided to launch a pre-emptive strike on the problem and ordered a space-grade Polyimide Thermofoil flexible heater:
This will be wrapped round the motor casing, with a layer of space blanket as insulation, and held in place with some heat-shrink tubing.
The effective area of the heater is 46.54 in2 (300.257 cm2), and its resistance is 64Ω. A quick calculation revealed that at 12V, it'd be running at 0.1875A and pumping out 2.24W - a watt density of 0.05W/in2, or 0.0078W/cm2.
Once we've got the rocket casing and heater in a tight embrace, we'll test to see just how much juice we need, and for how long, to the keep the temperature up.
We have three options: pre-heat on the ground, heat during the ascent phase, or a combination of both. Whichever ultimately proves necessary, it won't impact on the Vulture 2's weight, since any batteries will be external.
If we do heat during the ascent phase, we'll have to work out an umbilical system to supply power to the heater, and which will detach easily when the aircraft launches.
We're sure readers have some bright ideas as to how that can be done with the minimum of fuss.
4: Fantastical flying truss
As the above vid shows, we've done some testing to see just how our flying truss will, er, fly, and now have a definitive design, seen here in our lovingly-crafted one-quarter scale model:
You'll note it's sprouted a tail, which helps keep the truss orientated into the wind. We've just ordered the carbon fibre rods and fittings to construct the full-fat, two-metre long truss, so we'll do more testing when we've put that together.
What we can't do at this stage is add the titanium launch rod, since we'll need the Vulture 2 to work out its exact positioning.
5: Mission electronics
We recently took a major step towards resolving the thorny problem of just how to trigger the Vulture 2's motor at altitude when reader Anthony Stirk offered to put together one of his Swift Rev2 boards - designed for long-duration High Altitude Ballooning (HAB) missions:
The components are:
- ATMega644 running at 8Mhz
- uBlox MAX-6 GPS
- Sarantel Antenna
- Radiometrix 300mW HX1 Module for APRS (Automatic Packet Reporting System)
- Radiometrix 10mW NTX2 Module for RTTY (radioteletype)
- BMP085 Pressure Sensor
- Triple DS18B20 temperature sensors
- Header for UART (Universal Asynchronous Receiver-Transmitter) camera
- 3.3V and 5V power rails
Critically, the uBlox MAX-6 GPS is good to 50km (164,000ft), so we can use it to fire the Vulture 2 custom igniter via one of the board's five general purpose input/outputs (GPIOs).
Neil Barnes - he of the barometric altimeter almost sucked to death in the REHAB chamber - has agreed to do the coding, so we're in business.
We've decided to add an accelerometer to the mix, to help us detect balloon burst. As we previously reported, this will, in parallel with the GPS – which can also obviously be used to detect drop in height – act as a failsafe ignition trigger in the event of premature balloon burst.
When the big day comes, we'll be packing a spare meteorological balloon, so we can go for two flights if necessary. This option impacts on the Swift rocket motor ignition parameters, which are:
- Arm ignition system at 60,000ft (18,300m).
- Fire rocket motor at [classified].
- First launch: In case of premature balloon burst, as indicated by accelerometer and/or GPS, abort launch.
- In case of abort, or ignition failure at launch altitude, ignition system safety shutdown after two hours, or when altitude falls below 40,000ft (12,200m), whichever comes first.
- Second launch: In case of premature balloon burst, as indicated by accelerometer and/or GPS, fire motor immediately.
The Swift will also be logging flight data, and may be required to control the rocket motor heater. If all this proves an excessive workload for the board, we'll consider spreading the load to a second unit.
So, that's currently where we're at with LOHAN. As ever, your comments and or suggestions are warmly welcomed, preferably down the ballocket mosh pit. ®
Further LOHAN resources:
- New to LOHAN? Try this mission summary for enlightenment.
- You can find full LOHAN coverage right here.
- Join the expert LOHAN debate down at Reg forums.
- All the LOHAN and Paper Aircraft Released Into Space (PARIS) vids live on YouTube.
- For our SPB photo archive, proceed directly to Flickr.
- We sometimes indulge in light consensual tweeting, as you can see here.