This TID computation tool can be user by 2 different space communities

I. The New Space community

Most of New Space (NS) actors don’t have accurate and powerful software, and no radiation expert able to run ‘correctly’ these codes. The TID Computation tool can be run by any project members, in order to get very fast an accurate approximation of their TID level for their mission.

For a given mission (altitude; inclination; lifetime), and a for a given small satellite characterized by 6 ‘equivalent thicknesses’ in mm Aluminium (Al), the TID Computation tool will return, very fast in few seconds, the Total Ionizing Dose level deposited within a Silicon detector, located inside a Solid Cube Box.

Of course, this TID level could be considered as a worst-case value. Here, the innovation is to get the Solid Cube TID level, for any orbit in few seconds, and not the Solid Sphere TID level as it is done currently, leading to a huge overestimation of the TID level.

In appendix, example of TID curves for Solid Cube and Solid Sphere are given to show the relative factor

II. The "Classic" Space community

Even if they have accurate and powerful radiation software, and radiation experts able to run it correctly, the TID Computation tool can be very useful for project engineers, quality engineers, parts procurement engineers as well.

• Typing 5-7 mm Al, TID Computation tool will return a reliable TID range for a classical satellite
• Typing 20 mm Al, TID Computation tool will return the minimum TID Level requirement for your mission
  

The full Inclination vs Altitude "orbit space" is investigated. Each point is a full mission ( 200 orbits & 300 points/orbit ) in order to characterize the South Atlantic Anomaly on LEO orbits.

Environment models used are:

• Trapped electrons: AE8 Solar Maximum /
• Trapped Protons: AP8 Solar Minimum /
• Solar protons: ESP model @ 90% confidence level /
• Lifetime 11 years, to cover a full solar cycle

In order to be more representative of the reality, and to avoid TID level overestimation TID Levels are calculated at the center of an Al Solid Cube (fig.1-b), and not inside a Solid Sphere (fig.1-a). As a reminder, TID Depth Curves for both shielding Solid Sphere & Solid Cube is given (fig.2)

A CubeSat satellite, or minisat, is a compact structure and looks like a Solid Cube Box.

In early 1980’s, the Six Sectors method was currently used: Estimate each thickness along each direction ( X+ , X- , Y+ , Y- , Z+ & Z- ), read the dose arriving through each face (4/6 ) on the Solid Sphere Depth Curve. Using the Solid Sphere curve will provide an important TID level overestimation.

From few years, we observe that New Space companies are back to this old 80's method, in order to save engineering and software expenses

Then, the TID Computation tool is based on this 80’s method, but the Ray Tracing for a solid cube is integrated, and then, the return TID level is given at a center of a Solid Cube by an analytical formula.

Example: Based on a Geostationary environment, considering only the trapped electron AE8 Solar maximum, results are as follow:

Red Line : Solid Sphere calculated by 3D Monte Carlo Reverse method

Green Line : Solid Cube calculated by analytical ray tracing formula, used in the TID Computation tool

Green Triangle : Solid Cube calculated by 3D Monte Carlo Reverse method

Scope of the SEU Computation tool

The design of digital electronics travelling through space onboard satellites requires being able to calculate the Single Event Upset (see appendix II) rate induced by Galactic Cosmic Rays and Trapped Protons (see appendix below).

The main objective of the SEU Computation tool is to offer a simple, easy to use and very fast tool, for the ‘NEW SPACE’ community.

In space, SEU rates can vary from 100 to 104 SEU/device.day. The SEU Computation tool will help to design and optimize the SEU Detection/correction circuitry necessary for the satellite design.

Another key point is that the SEU Computation tool can be run by any ‘NEW SPACE’ project member, without any expert level knowledge in space radiation effects.

Two functions are available in the SEU Computation tool :

FUNCTION # 1: SEU RATE ROUGH ESTIMATION

• In the case where you do not have any experimental data for your part: the SEU Computation tool will return the SEU rate on your chosen orbit, in SEU/Mbit.day by using a 72 Mbit SRAM “witness” part. This function makes it possible to quickly compare two different orbits from the SEU stress point of view. This function could be very interesting for New Space designers.

FUNCTION # 2: SEU RATE CALCULATION FOR A PART

• In the case where you do have experimental data for your part (both heavy ions & protons, you can get this data from literature or have your own testing data): the SEU Computation tool will calculate quickly an accurate SEU rate on your orbit for that specific part.
• This function # 2 could be useful even for a ‘CLASSIC SPACE’ design engineer, project engineer, Quality engineer, Parts Procurement engineer, … because you don’t need to be an expert to run the SEU Computation tool
• This function # 2 could also be useful for ‘PARTS DATABASE’ management, in order to sort parts able to withstand a specific mission. This will help the designer who is not an expert in the space radiation environment.

Orbit altitude range: [ 100 km ; 36 000 km ]

Inclination range: [ 0° ; 98° ]

Shielding Thickness: [ 0.1 mm Al ; 15 mm Al ]

SEU Computation tool accuracy vs OMERE

The absolute reference for SEU calculation Rates is OMERE 5.2.5. Therefore, The SEU Computation tool 1.0.5 is compared to OMERE in order to quantify the accuracy of The SEU Computation tool approximation tool. About 76 calculations were performed on the “witness” PART_A, using both The SEU Computation tool 1.0.5 and OMERE 5.2.5. Results are summarized in the following figure:

The SEU rate is calculated as follows:

Detailed SEU Rate calculations results are given in paragraph VIII. We can have a look at each contribution to the Total SEU Rate:

• Galactic Cosmic Rays contribution: GCR ISO, Solar Minimum (worst case)
• Trapped Protons: AP8, Solar Minimum (worst case)

ISO SEU RATE MAPS ON ORBITs

Running the SEU Computation tool for various orbits:

• Altitude : 100 Km to 10000 km with 100 km step, then 10000 Km to 36000 with 1000 km step
• Inclination : 0 to 90° with a 2° step

For each part, PART_A, PART_B and PART_C, the following ISO SEU RATES contours are calculated for two shielding thicknesses : 4 and 10 mm Al

Conclusion

The SEU Computation tool is an interesting tool for the NEW SPACE community, for the following reasons:

• Easy to use, even if you are not very familiar with space radiation
• Limited parameters: chose “altitude” and “inclination” and no more
• Verry fast run time, less than 0.1 second for any orbit
• Accuracy acceptable for an approximation: -2% ; +6%
• Useful tool to compare rapidly various orbits. Interesting in case of reusing existing equipment for other missions: more severe? less severe? equal?
• PROFIT V2 integrated into The SEU Computation tool, in case you only have heavy ions data
• A rough SEU rate is provided on your orbit, in case you don’t have any data
  

The SEU Computation tool is only an approximation based on a complex Figure of Merit (FOM) algorithm, with the goal of providing “easy to use” tools for the New Space community. For any accurate SEU rate calculation requirements, it is recommended to use OMERE 5.2.5 which remains the absolute reference.