Chapter 1114 The Problem of Going to the Star with Ion Propulsion
Meng Zhizhong’s attitude is indeed very correct.
But a good attitude does not fundamentally solve the problem.
The so-called bicomponent propulsion system is essentially a chemical propulsion system that uses liquid methyl hydrazine and dinitrogen tetroxide as fuel and oxidant respectively.
To put it more broadly, rocket engines are essentially a two-component 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 shortcomings...
The rest are almost all shortcomings.
First of all, fuel is limited. In fact, the life of a satellite depends to a large extent 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, it is difficult to perform particularly fine control.
Furthermore, 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 for 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 for independent orbit determination testing...
In short , on 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.
The effect is hardly 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 the current situation, even in the past five years, there is no There are other better options. Other satellites are either clearly functional satellites that cannot be used for testing, or they cannot be tested individually or in dual-satellite systems..."
"You cannot launch a batch of satellites separately, just for the purpose of testing. Testing an autonomous orbit determination is just a proof of principle, right?”
In fact, in the future commercial space era, not to mention satellites, even rockets can be tested.
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.
So there is nothing wrong with Meng Zhizhong’s caution.
“Actually, Mr. Chang, you don’t have to worry so much. All the 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 changes under sufficient conditions. Just run the data.”
In fact, Chang Haonan was already planning to nod——
After all, my current main focus still has to be on the high bypass ratio turbofan engine and relay communication links. Other projects can provide some support at most, but it is impossible to take the lead.
"Then..."
But, at the moment of speaking.
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 equipment 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 indeed very small.
But for satellites, the resistance of the space environment is almost negligible anyway, and a smaller thrust is just a longer working time.
In general, 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 independent orbit determination technology...
It was a perfect match.
In the previous life, China’s electric thrusters did not actually go to space until the 2010s, but judging from the actual situation, ground testing actually started very early.
If some additional resources can be provided, it should not 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 take about a year... …”
“Isn’t that just in time?”
Chang Haonan patted the armrest of the seat:
“Electric propulsion technology is the core technology of future spacecraft, and The autonomous orbit changes work well together, and we can put a group of satellites together for testing together.”
“Although it will take a year or two to wait on the ground, the testing work can be carried out in a centralized manner. Isn't it better than taking a ride on Practice No. 7 and only releasing a set of data every few months or even a year?" 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..."
"Huh?"
Chang Haonan was also stunned.
“The other technical routes of electron bombardment are good. The lifespan is a bit low among electric propulsion, but it is enough if you don’t engage in deep space exploration... but it consumes too much power.”
Meng Zhizhong explained:
“Don’t talk about small satellite platforms... The Dongfanghong 3 satellite’s stable power supply capacity in low-Earth orbit is only 1.7kW. As soon as LIPS-200 is turned on, the single propulsion power will be used. About 1.5 kilowatts...the remaining 200W, not to mention the mission load, even the on-board control system cannot be maintained stably..."
Chang Haonan knows this data:
"The highest What about the power supply? "
Chang Haonan has at most done some research on satellite payloads. As for the entire satellite system, although it is impossible to completely understand it, he only has a vague understanding of it.
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 a strong unusual Linear 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 is also closely related to the load output voltage.
Only at a certain voltage, the output power can reach the 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, the energy consumption is relatively low -
If you really want to pack so many devices, the volume of Dongfanghong 3 will not be able to fit in.
So 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...
It’s not impossible.
“Ahem——”
Chang Haonan cleared his throat:
“We have a maximum power point tracking technology in the aviation field that can adjust solar energy in real time according to load conditions. The output voltage of the power supply keeps it relatively stable 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 achieve changes in 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 while, he didn't even have time to feel the joy.
The first thing that came up was curiosity:
"As a digression... Why do you guys who build airplanes need this kind of technology? Isn't there an APU, and the engine itself can provide stable power supply?"
< br>"..."
The other party's brain circuit also made Chang Haonan a little confused.
In fact, this is one of the basic technologies used in solar-powered long-endurance aircraft twenty years later.
But it’s really not easy to explain right now.
So, he had to say haha:
“Isn’t this just because it is useless for airplanes, so I just remembered it...”
Meng Zhizhong’s doubts Apparently not completely gone.
But at this moment, the surprise that I didn’t feel just now has gradually taken over the dominant mood:
"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 is enough to install the LIPS-200!"
Chang Haonan nodded:
"Then I can verify this maximum power point tracking technology on Practice No. 7..."
(End of this chapter)