Chapter 1114: The Problem of Ion Propulsion on Satellite

Meng Zhizhong's attitude is indeed very correct.

But a good attitude cannot fundamentally solve the problem.

The so-called bipropellant propulsion system is essentially a chemical propulsion system that uses liquid methylhydrazine and nitrogen tetroxide as fuel and oxidant respectively.

To put it in a broader sense, a rocket engine is essentially a bipropellant propulsion system.

As you can imagine, its characteristics are very obvious——

The advantage is that the thrust is large enough.

Especially for a satellite, orbit change and attitude adjustment can be completed in a very short time.

As for the disadvantages…

The rest are almost all shortcomings.

First, fuel is limited. In fact, the life of a satellite depends largely on how long the fuel it carries can be used.

Secondly, as you can imagine, the stability of chemical combustion is actually difficult to guarantee, even in a fuel cell, so it is difficult to carry out particularly fine control.

Moreover, the weight of the fuel itself is not low compared to the size of the satellite, which is almost a complete waste in terms of function.

In addition, as the fuel is consumed, the satellite's center of gravity will also change, adding a lot of load to the onboard control system out of thin air.

Not to mention that the liquid in the half-full fuel tank will inevitably slosh when the satellite moves, further affecting the accuracy of the movement...

Although people have made many improvements to this end, such as the new attitude adjustment algorithm tested by Chang Haonan on Qingluan II, these drawbacks cannot be eradicated.

As a communication verification satellite, Shijian-7 does not require particularly stringent communication accuracy and orbit change frequency, but this does not meet the requirements of autonomous orbit determination testing...

In short, under the premise of ensuring the normal implementation of the Practice No. 7 mission itself, there are actually very few opportunities left for Meng Zhizhong and others to use for testing.

The effect is hard to say that it is very satisfactory.

Moreover, the limited number of times has to be distributed over the entire life cycle of the satellite, which is within the next 3-5 years.

Although the construction of BeiDou-2 has not yet begun and this technology is not in a hurry to be put into use, people who often do research will know that this piecemeal testing method is not conducive to the normal progress of the project.

After listening to Chang Haonan's concerns, Meng Zhizhong also expressed his helplessness:

"Of course I know this... But let alone right now, even in the past five years, there are no better options. Other satellites are either clearly functional satellites that cannot be used for testing, or they cannot be tested individually or in a binary system..."

"You can't just launch a batch of satellites just to test autonomous orbit determination, and it's just a proof of principle, right?"

In fact, in the future era of commercial space flight, not to mention satellites, even rockets can be tested by flight.

But that’s largely because there’s no psychological pressure to spend investors’ money, and there’s a higher tolerance for failure and accidents.

The current resources and situation of China's aerospace industry certainly do not allow this to happen.

So there is nothing wrong with Meng Zhizhong's caution.

"In fact, you don't have to worry so much, Mr. Chang. All the operating rights of the satellite, including the equipment, are 100% handed over to you. Chief Engineer Fan and his team only need to obtain some orbit change operation data when conditions are sufficient."

In fact, Chang Haonan was about to nod his head at this moment——

After all, my current main focus is still on the high bypass ratio turbofan engine and the relay communication link. Other projects can at most provide some support, but it is impossible for them to take the main responsibility.

"That……"

But, the moment he opened his mouth.

He suddenly remembered something he had heard when he first came into contact with the Ocean No. 1 project two years ago.

"Academician Meng, I remember that the Academy of Sciences seemed to be developing an electric propulsion device two years ago..."

Electric propulsion, due to its low dependence on working fluid and simpler structure, has almost no disadvantages brought by chemical propulsion, and can produce an astonishingly high (four-digit) specific impulse.

The only problem is that the thrust is really small.

But for satellites, the resistance of the space environment is almost negligible anyway, and a smaller thrust will only result in a longer working time.

Generally speaking, the working life of electric propulsion equipment, which is generally around 10,000 hours, is definitely much more robust than traditional solutions.

If it is an ordinary satellite, the long orbit change time may bring unnecessary pressure to the ground measurement and control system.

However, what the other party wanted to test was the autonomous orbit determination technology...

Simply perfect.

In the past, China's electric propulsion was not actually launched into space until the 2010s, but in reality, ground testing actually began very early.

If additional resources can be provided, it should not be a problem to advance the time node by a few years.

However, Meng Zhizhong seemed to understand this better than Chang Haonan:

"I know that the Jincheng Institute of Physics' LIPS-200, an electron bombardment ion propulsion system, has a thrust of 40mN, a specific impulse of 3000s, and a lifespan of 1.2 hours. It is currently undergoing long-life ground assessment and verification, which is expected to last about a year..."

"Wouldn't that be just in time?"

Chang Haonan patted the armrest of the chair:

"Electric propulsion is the core technology of future spacecraft, and it works well with autonomous orbit change. We can combine it together and send a group of satellites up there to test it together."

"Although we have to wait for a year or two on the ground, the testing work can be carried out intensively. It's better than taking a ride on Practice 7 and only producing a set of data after several months or even a year, right?"

Meng Zhizhong scratched his head upon hearing this, revealing a somewhat distressed expression:

"LIPS-200 actually has no plans to be launched into space in the short term..."

"what?"

Chang Haonan was also stunned.

"The electron bombardment technology is fine in other aspects. Its lifespan is a bit low among electric propulsion technologies, but it is sufficient if we don't do deep space exploration...but the power consumption is too high."

Meng Zhizhong explained:

"Forget about the small satellite platform... The Dongfanghong 3 satellite has a stable power supply capacity of only 1.7kW in low-Earth orbit. Once LIPS-200 is turned on, the propulsion power alone will consume about 1.5 kilowatts... With 200W left, not to mention the mission payload, even the onboard control system cannot be maintained stably..."

Chang Haonan knew this data:

"What about the maximum power supply?"

At most, Chang Haonan has done some research on satellite payloads. As for the entire satellite system, although he cannot be completely clueless, he only has a vague understanding of it.

At least he is definitely not as good as the expert Meng Zhizhong.

The latter answered almost without hesitation:

"2.3kW...but this data is meaningless?"

The output of the satellite-borne solar power source has a strong nonlinear characteristic. It can be regarded as a constant current source at low voltage and a constant voltage source at high voltage. Therefore, in addition to being affected by external factors such as light intensity and temperature, the output power is also closely related to the load output voltage.

Only at a certain voltage can the output power reach its maximum.

That is 2.3kW.

But obviously, the conditions to achieve this indicator are very harsh.

The working conditions of onboard equipment are complex and it is impossible for them to be so stable all the time.

That is why Meng Zhizhong commented that it is meaningless.

The 1.7kW value is a range that engineers have calibrated as "highly achievable" based on the characteristics of the satellite's power load.

In fact, the satellite-borne equipment of this era generally has poor performance and is also very large in size and weight.

Correspondingly, energy consumption is also relatively low——

If you really want to cram in so much equipment, even the size of Dongfanghong 3 won’t be enough.

Therefore, 1.7kW is sufficient for general loads, such as Practice No. .

It’s just that ion propulsion on satellites is indeed a huge electricity consumer, so this gap was created.

but……

It's not impossible.

"Cough-cough-"

Chang Haonan cleared his throat:

"We have a maximum power point tracking technology in the aviation field, which can adjust the output voltage of the solar power source in real time according to the load conditions, so that it can be kept relatively stable near the maximum power point."

"In fact, it is just to modify the main error amplifier circuit of the direct energy transfer power supply system, add a D/A converter and a corresponding control unit, and the reference voltage can be changed... The cost is that the life of the power supply will be reduced, but in fact, it is difficult for ordinary satellites to work until the power supply is damaged, so the impact may not be that great..."

For Meng Zhizhong, this was a complete surprise.

It's like you just have two dollars in your pocket and you're looking for somewhere to spend it so you buy a beer.

When he opened the bottle cap, he found that he had won 200,000 yuan.

For a moment, he didn't even have time to feel the joy.

What comes to mind first is curiosity:

"Let me digress... Why do you aircraft engineers need this kind of technology? Don't we have APUs? And the engines themselves can provide stable power supply?"

"..."

Chang Haonan was also a little confused by the other party's train of thought.

In fact, this is one of the basic technologies used in solar-powered long-endurance aircraft twenty years later.

But it’s not easy to explain right now.

So he just laughed it off:

"Isn't it because it's useless for airplanes that I just thought of it..."

Meng Zhizhong's doubts obviously did not completely disappear.

But at this moment, the surprise that I didn't feel just now has somewhat belatedly dominated my emotions:

"If it's really as you said, then we don't have to be particularly precise. As long as we can increase the power to more than 2.0kW, it will be enough to install LIPS-200!"

Chang Haonan nodded:

"Then I can verify this maximum power point tracking technology on Practice No. 7..."