Chapter 1114: Problems of Ion Propulsion on Satellites

Meng Zhizhong's attitude was indeed very upright.

But having a good attitude does not fundamentally solve the problem.

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

Speaking more broadly, a rocket engine is essentially a two-component propulsion system.

So it can be imagined that 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 of all, fuel is limited. In fact, satellite life span depends largely on how long the fuel carried can be used.

Secondly, it is conceivable that the stability of chemical combustion is actually difficult to guarantee, even if it becomes a fuel cell, so it is difficult to perform particularly refined control.

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

In addition, as fuel is consumed, the center of gravity of the satellite 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 later, further affecting the accuracy of the movement...

Although people have made many improvements to this, such as the new attitude adjustment algorithm tested by Chang Haonan on Qingluan 2, these drawbacks still cannot be eradicated.

As a communication verification satellite, Shijian No. 7 does not require particularly stringent communication accuracy and orbit change frequency, but this is not consistent with the requirements of independent orbit determination testing...

In short, under the premise of ensuring that the mission of Practice No. 7 is carried out normally, there are actually very few opportunities left for Meng Zhizhong and the others to test.

It’s hard to say that the effect is very satisfactory.

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

Although Beidou II has not yet started construction, and there is no rush to put this technology into use, people who often do research will know that this piecemeal testing method is actually not conducive to the normal advancement of the project.

After hearing 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 is no other better option. Other satellites are either clear functional stars that cannot be tested, or they cannot be tested individually or in dual-satellite systems... …”

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

In fact, in the future commercial aerospace era, not to mention satellites, even rockets can be used for testing.

But that's largely because there's no psychological pressure to spend investor money, and there's a greater tolerance for failure and mishaps.

The current resources and situation of China Aerospace certainly do not allow this.

Therefore, Meng Zhizhong's caution is not wrong.

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

In fact, Chang Haonan was already planning to nod at this moment——

After all, my current main focus still has to be on the large bypass ratio turbofan engine and relay communication links. Other projects can provide some support at most, but it is impossible to take the lead.

"That……"

But, the moment he spoke.

He suddenly remembered something he heard when he first came into contact with the Ocean One project two years ago.

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

Electric propulsion, because it relies less on working fluids and has a relatively simple structure, has almost no disadvantages caused by chemical propulsion, and can produce surprisingly high (four-digit) specific impulses.

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 is just a longer working time.

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

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

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

A perfect match.

In the previous life, China's electric thrusters did not actually go to the stars until the 2010s, but judging from the actual situation, ground testing actually started very early.

If some additional resources can be provided, it shouldn't be a problem to advance the time node a few years.

However, Meng Zhizhong seems to know more about this than Chang Haonan:

"I know that the LIPS-200 of the Jincheng Institute of Physics, an electron bombardment ion propulsion system, 40mN thrust, 3000s specific impulse, and a lifespan of 12,000 hours, is currently undergoing long-life ground assessment and verification, and it is expected to be conducted for about a year... …”

"Isn't that just in time?"

Chang Haonan patted the armrest of the seat:

"Electric propulsion technology, the core technology of future spacecraft, works well with autonomous orbit changes. It can be combined together and a group of satellites can be put up for testing together."

"Although it will take a year or two to wait on the ground, the testing work can be carried out intensively. It is better than taking a free ride on Practice No. 7 and only releasing a set of data every few months or even a year, right?"

Meng Zhizhong scratched his head when he heard this, showing a somewhat troubled expression:

"LIPS-200 actually has no plans to go to space in the short term..."

"ah?"

Chang Haonan was also stunned.

"The electronic bombardment technology is good compared to other technologies. The lifespan is a bit low compared to electric propulsion, but it is enough if you don't engage in deep space exploration... but it consumes too much power."

Meng Zhizhong explained:

"Not to mention the small satellite platform... The Dongfanghong 3 satellite's stable power supply capacity in low-Earth orbit is only 1.7kW. Once the LIPS-200 is turned on, the propulsion power alone will use about 1.5kW... The remaining 200W, don't Speaking of mission loads, even the on-board control system cannot maintain stability..."

Chang Haonan knows this data:

"What about the maximum power supply?"

Chang Haonan now has at most some research on satellite payloads. As for the entire star system, although it is impossible to have a blind eye, he only has a partial understanding.

At least certainly not as good as the expert Meng Zhizhong.

The latter answered almost without thinking:

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

The output of the spaceborne solar power supply has strong nonlinear characteristics. 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 It 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, in order to achieve this indicator, the conditions are very demanding.

The working conditions of onboard equipment are complex and cannot always be so stable.

That's why Meng Zhizhong evaluated it as meaningless.

1.7kW is a range that engineers have calibrated based on the characteristics of the satellite's electrical load and is "probably achievable".

In fact, the performance of spaceborne equipment in this era is generally poor, and the size and weight are also very large.

Correspondingly, energy consumption is also relatively low——

If you really want to pack so much equipment, the size of Dongfanghong 3 will not be able to fit in.

Therefore, 1.7kW is enough for general loads, such as Shijian No. 7.

It's just that ion propulsion is indeed a large power consumer on the satellite level, so there is a gap.

but……

There is no way.

"Ahem——"

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 supply in real time according to the load condition, so that it can be maintained relatively stably near the maximum power point."

"In fact, it is to modify the main error amplification circuit of the direct energy transmission power supply system and add a D/A converter and corresponding control unit to realize the change of the reference voltage... The price is that the ultimate life of the power supply will be reduced, but in fact generally It is also difficult for satellites to work until the power supply is damaged, so the impact may not be that big..."

For Meng Zhizhong, this was a complete surprise.

It's like you just had two change in your pocket and wanted to find a place to spend it, so you bought a bottle of beer.

As a result, I opened the bottle cap and found that I had won two hundred thousand dollars.

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

What came first was curiosity:

"To digress...why do you guys need this kind of technology when building airplanes? Doesn't it have an APU, and the engine itself can provide stable power supply?"

"..."

Chang Haonan was a little confused by the other party's thinking.

In fact, this was one of the fundamental technologies used in solar-powered long-endurance vehicles twenty years later.

But it’s really not easy to explain right now.

So, he had no choice but to say haha:

"Isn't this just because it's useless for airplanes, so I just remembered it..."

Meng Zhizhong's doubts obviously did not disappear completely.

But at this moment, the surprise that I didn't feel just now has already taken over the dominant mood somewhat unconsciously:

"If I really follow what you said, it doesn't have to be particularly precise. As long as the power can be increased to more than 2.0kW, it will be enough to install the LIPS-200!"

Chang Haonan nodded:

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