Dear readers,

The last couple of months have been all about creating the main structure of down-scaled space capsule TDS80. This capsule is headed for space (112 km) during the summer of 2014 on the HEAT2X launch vehicle.

You can find the preliminary trajectory documents here

If you are a follower of this blog you will understand the decisions made for the general geometry - based on internal subsystems, wind-tunnel testing and aerodynamics. If not, please check out some of these blog posts:

Video - structural assembly principles

TDS80 capsule subsystems

The HEAT2X launch vehicle has the same diameter as HEAT1X which is app 640 mm and thus the capsule will have to fit as the payload nosecone with the same diameter. Early it was decided to pick out only a certain number of systems to be added and tested on the TDS80. By doing so we will be able to examine relevant systems accordingly to the mission scenario (suborbital shot to space and back) and likely increase the chances of success by not having too much going on.

The launch escape system (LES) is not being added this capsule. A scaled down LES is complex to make with tiny explosive bolts and separations systems and if this part does not work – nothing will happen later in the important phases such as re-entry stability. Re-entry is the main focus, besides long distance two-way communication. For the first time I have a change to actually get a capsule atmospheric re-entry - which cannot be simulated on Earth – at least not by us.

To get the same re-entry stability as the full scale capsule I have to keep the same ballistic coefficient (BC). Using this BC formula,



..and changing the diameter from 1.6 m to 0,64 m while estimating a similar drag coefficient (Cd) the mass changes from 500 kg (full scale) to 80 kg (scaled). In other words the TDS80 scaled capsule must have a mass of 80 kg.

The production of this capsule is done in corporation with the rest of the crew working communication, power-budgets, cameras, navigation and avionics. However, I decided to create and open architecture structure which will be able to accommodate whatever interior installation issues these guys are presenting in the future.

René Olsen and I have so far fulfilled our plan of finishing the main structure and the following images will show you the main steps of that process:

One of the initial sketches showing subsystems and main structure assembly ideas. Image: Kristian von Bengtson

A whole bunch of sketches was done to get some kind of initial idea of the size, subsystems layout and how to actually produce the capsule while keeping an open structure for further development and potential changes. One of the main concerns was the small size and the ability to easy install and replace avionics. This led to the decision that all external side panels will have to accommodate being taken on and off - no welding, only on the main structure.

Next step - going from detailed sketch to Solidworks CAD modeling. Image: Kristian von Bengtson

TDS80 capsule exploded view. Image: Kristian von Bengtson

For me, next step is always going from sketch to Solidworks creating a fast but precise CAD-model for subsystems spacing evaluation and for next step laser cutting in aluminum. The few parts that makes up the capsule structure will be added the bottom heat shield dish - which was ordered from a company specializing in end-cap parts.

Exported files via Solidworks for basic laser cutting. Image: Kristian von Bengtson

Happy days!!! After waiting weeks the parts arrived and the first test assembly can be performed with much joy and singing. Image: Kristian von Bengtson

Finally, getting the piece is a special feeling. CAD drawing and sketches are no match for this real life physical manifestation of objects.

The geometry of laser cut parts on the heat shield. Image: Kristian von Bengtson

Even though the laser cut parts and heat shield are professionally made with high precision they always deviate from its measurements due to its structure and manufacturing processes. This has to be taken into account and adjusted (with a hammer and angle grinder!)

The remaining parts rolled for side structures (to hold external side panels). Image: Kristian von Bengtson

The side structure of the capsule is likewise flat laser cut parts which have to be manually rolled to obtain the correct cone shape. Solidworks is a big help to flatten cone-shapes for laser cutting but the rolling procedure does require some expertise and hands-on skills. Always remember to pre-bend (with a rubber hammer and a block of wood) the edges of such a cone - since the roller cannot reach the end-pieces.

The chute and ballute attachment points with re-enforcement. Image: Kristian von Bengtson

The capsule will hold a ballute ensuring stable atmospheric re-entry and finally a drogue for the last phase and splashdown. Each of these drag devices have to two connector point in the top of the capsule (where a top-dome will be added). The main structure is made from 8 mm aluminum and is not strong enough to obtain the forces - during a worst case scenario deployment. Each of these four structure are added 2 mm steel on each side to increase the load capability.

Assembly of side cones to main structure. Image: Kristian von Bengtson

The side cones are attached and fitted the main structure and hold in place for welding. Before doing so, the welding joints are cut open for better welding connection.

TIG-welding the main structure. Image: Kristian von Bengtsion

Side bars added for eventually holding the external side panels in place. Image: Kristian von Bengtson

In total there will be eight side panels covering the capsule. These panels will have to be bolted on all four sides (of each panel) and this requires additional side structures running down along the main structure. The dimensions of these bars of extracted from Solidworks but has to be tailored individually to each side because there is always irregularities on hand made prototypes like this.

Main structure welding on heat shield. Image: Kristian von Bengtson

Welding and heat shield brush-up. Image: Kristian von Bengtson

In many locations it is not possible to make use of TIG-welding and in those places MIG-welding was used for the final assembly. There is plenty of structural strength in only a few long seems and if all joints are fully welded we are likely to end up having structural deformation on the entire capsule.

Center compartment for ballute, drogue and uprighting. Image: Kristian von Bengtson

The entire center volume of the capsule is dedicated the chamber for ballute, drogue and floater device. To keep the best options for avionics and subsystems installation we decided not to permanently weld this chamber into the structure - but rather spend an extra effort making it detachable using bolts on the structure.

Bottom chute chamber attachment point. Image: Kristian von Bengtson

The chute chamber will be bolted to the bottom and side of the structure keeping it firmly in place but maintaining an open structure for further development.

TDS80 dec 2013. Image: Kristian von Bengtson

The images above is the TDS80 in it current state - the main structure is done. A test side panel has been produced and the internal bars for holding the main avionics boxes are likewise done.

Next step - TDS80. Image: Kristian von Bengtson

The next step is a detailed examination of all subsystems and understanding how to attach these to the capsule. Now the main structure is done we will have time for looking into ballute-design and perform testing on top-lid deployment using airbag devices.

René and I are so far satisfied with the development of this capsule and working aluminum is a blast. I cannot wait for the full size aluminum capsule to begin production.

But first we have to see this little guy fly all the way into space and land safely in the ocean hopefully providing us with a lot of useful data for coming capsule development.

And dont forget - the name is still up for debate!

Have a great weekend!

Ad Astra

Kristian von Bengtson