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Solar Spacecraft Ion Propulsion Power Supply

I knew I wanted to be an Electrical Engineer at age 12 when, in 1961, the first Mercury space capsule was launched and I watched the in-depth coverage on TV all day. I was amazed by the electronics I saw inside the capsule for communications, guidance/control, and life-support as well as lighting. I wanted to be a part of that. The electrical power was supplied by various combinations of 1,500-watt and 3,000-watt batteries. Water was used to cool the electrical systems.

We've come a long way since then from chemical propulsion to Ion engine propulsion, which is electrical propulsion. This type of propulsion needs a very stable power supply. This type of system increases the electrical power demand on the spacecraft power supply by 10s of kW and usually solar array regulator technology is the power source of choice.

Artist's conception of BepiColumbo spacecraft near the planet Mercury  (Image courtesy of ESA)

Artist's conception of BepiColumbo spacecraft near the planet Mercury
(Image courtesy of ESA)

Solar electric propulsion (SEP) could be used to make the spacecraft cruise from Earth to Mercury, such as in the BepiColombo Mission to explore Mercury. (Solar power makes sense since Mercury is the closest planet to the Sun.) A power supply system that does not require a battery can be used since Ion Thrust is not needed (since the Sun's massive gravity will accelerate the spacecraft), so a great deal of mass is saved. As it turns out BepiColombo will use the gravity of the Earth, Venus, and Mercury in combination with the thrust provided by solar-electric propulsion (SEP). The final design consists of electric propulsion and traditional chemical rocket units. The spacecraft is now being built and tested by the European Space Agency (ESA).

A new concept of a Sequential switching shunt maximum power regulator (S3MPR) made up of a sequential switching shunt regulator (S3R) which keeps the Solar Array (SA) voltage at its Maxim Power Point (MPP) and followed by a boost regulator producing a constant 100 V output to power the Electronic Propulsion (EP).

The S3MPR uses two independent regulators, one for the MPP1 bus (SA power) and the other for the EP Bus output voltage. The design uses the S3R for fast control of the SA power. For the EP output voltage control, the Weinberg Boost Regulator2 is used since it has a high power boost. (See Figure 1.)

Figure 1: Block diagram of the proposed Power Conditioning and Distributed Unit (PCDU)  (Image courtesy of Reference 1)

Figure 1: Block diagram of the proposed Power Conditioning and Distributed Unit (PCDU)
(Image courtesy of Reference 1)

The MPPT design is a modification of the Digital Perturb and Observe3 (DP&O) algorithm. The three independent Maximum Power Point Voltage (VMPP) signals generated by the MPPT controllers are fed to a majority voter circuit that finally gives the Main Error Amplifier (MEA) reference for the S3MPR block. The MEA of the MPP Bus is measuring a proportion of the SA voltage (Vmpp1) and compares it with the “ref” computed by the MPP control circuit detector. (See Figure 2.)

Figure 2: MPPT block diagram  (Image courtesy of Reference 1)

Figure 2: MPPT block diagram
(Image courtesy of Reference 1)

The main advantage this architecture provides is that the bus voltage is not modulated about the MPP. Only when a change in the SA operation point is detected does a calculation process get initiated. Amplifier AM acts upon the current limit of the UC1856 IC of the Boost regulators and prevents them from taking more current from the SA of the S3MPR.

The PCDU prototype (Figure 3).

Figure 3: The PCDU prototype is a 1 kW system (S3R + MPPT + MPP Bus capacitance Cmpp + EP Boost Regulators + Electronic Propulsion Bus capacitance Cep)  (Image courtesy of Reference 1)

Figure 3: The PCDU prototype is a 1 kW system (S3R + MPPT + MPP Bus capacitance Cmpp + EP Boost Regulators + Electronic Propulsion Bus capacitance Cep)
(Image courtesy of Reference 1)

This design can be used in future 100 V power busses on spacecraft. It has fast response to load changes and the bus transient voltage is well within spec so no battery or pre-regulator is needed. The building blocks are low-risk since they have 30 years of tried and true performance.

Steve T's dream (A result of my visit to the NASA Ames Research Visitor's Center recently.)

As I mused upon the Ion Propulsion engine, I steered my spacecraft towards the Moon, not using an Ion Propulsion system, but a traditional chemical engine.


And when I landed on the Moon, I was able to check an item off my “Bucket List.”

Then I went and explored the surface, bouncing around in low gravity to find that China rover and make sure they don't touch any of our Apollo stuff! (See my EDN article and slideshow: NASA says “Hands off our stuff on the moon!”)

References:

  1. Power System for Electrical Propulsion in Space Applications,E. Maset, E. Sanchis-Kilders, A. Ferreres, J.B. Ejea1, V. Esteve, J. Jordán, A. Garrigos, J.M. Blanes, A.H. Weinberg
  2. A BOOST REGULATOR WITH A NEW ENERGY.TRANSFER PRINCIPLE, A.H. Weinberg
  3. Perturb and Observe Digital Maximum Power Point Tracker for Satellite Applications, Brambilla, A., di Milano, P., Gambarara, M., & Torrente, G.

Editor's note: This article was originally published on EBN's sister publication EDN .

10 comments on “Solar Spacecraft Ion Propulsion Power Supply

  1. Hailey Lynne McKeefry
    February 23, 2014

    It sounds like a boon both for the industry and your bucket list!

  2. ic78man08
    February 23, 2014

    Ha–yes Hailey, for sure—-another item checked off!

  3. Eldredge
    February 23, 2014

    @script78man – Glad you were there to protect our national interests! How else would we find out about these acts of heroism?

  4. Nemos
    February 23, 2014

    I would like to ask (if I fully understand the article) if this “new” way of boosting can be used in veichles on earth?

  5. ic78man08
    February 23, 2014

    @Nemos—-Ion propulsion can be used on Earth. A normal rocket force has a huge mass times low acceleration. An Ion propulsion rocket engine has Force equal to a tiny mass times huge acceleration. On Earth, we can speed up or accelerate the small mass to produce enough force.

     

    So Ion propulsion forces tiny amounts of matter out the back of the engine at very high speed, where a conventional rocket engine sends out a huge amount of matter at slower speed.

  6. Houngbo_Hospice
    February 26, 2014

    Can Ion propulsion energy be used as a reliable renewal source of energy? If it can be used on earth, can it be produced in large quantities to power our household devices?

  7. Anand
    February 26, 2014

    The ion propulsion method used in spacecrafts has a very good overhead. Given that it takes little power from physical sources (takes entirely from solar energy), it can be used in different fields on earth.

  8. Wale Bakare
    February 27, 2014

    >>If it can be used on earth, can it be produced in large quantities to power our household devices?<<

    The concern over that is just cost. Many are running away from using such a source for generating electricity simply because of cost implication.

  9. Houngbo_Hospice
    February 27, 2014

    @Wale: The main problem with many alternative energy sources is that they are not cost effective and they mostly need huge incentives from the government to be produced.

  10. Wale Bakare
    February 27, 2014

    For an instance, one area UK government is really doing well. Trying to encourage householders as well and electric car users with Solar in particular. I think others should follow in that direction too – providing assistance like cash incentive. 

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