Still, Luna 25 has RTEGs and will serve for one year.
No worry, our next lander will be RTEG. If they hv no much instrument, why would they sending it.
Source- r/ISRO- u/ravi_ram
- Design framework of a Configurable Electrical Power System for Lunar Rover
A 50W electrical power system(EPS) design for a Lunar rover, which does not contain a radioisotope heater units, is presented. The design approach adopted, provides wide operational flexibility and enhances the survivability of the Rover, in the extreme environmental conditions and unpredictable terrains present over the moon. The design conserves the battery capacity for recovery from unfriendly terrains or for an extended power requirement by a scientific experimental payload.
The power bus design caters to the following operational features,
1. Minimal drain on the battery during the launch and transit phase of the mission. During this time rover is kept in power off condition and assembled to the drop-down platform of the lander. This is to ensure that, the battery is holding sufficient state of charge(SoC), during the initial phase to support the solar panel deployment and roll down from the lander drop down platform.
2.
Sleep and wake-up logics to address the initiation of automatic power shut-down, at the on set of lunar night and automatic power ON, whenever lunar day begins. The wake-up logic ensures that the activation of all rover circuitry happens only after the rover temperature builds up to a conjunctive level of 0C or more.
3. A feature to preserve the battery capacity before night falls, as the extreme cold survivability of battery enhances with higher state of charge. This is achieved by adding a command-able battery isolation, that makes the power bus to be sourced only from the solar panels.
4. Automatic disable of battery charging whenever the temperature is ≤ 0C. This prevents possible damage to the Li-ion battery, as charging at very low temperature can lead to a short mode failure of the cell[16]. The entire solar generation during this time is used for heating the battery as well as other rover electronic systems.
- Li-ion Batteries Study on survivability of 18650 Lithium-ion cells at cryogenic temperatures
Passive survivability of Commercially-off-the-shelf 18650 lithium-ion cells is tested in a thermal scenario similar to lunar night. Survivability of cells in particular and battery pack in general is crucial for resumption of function of any lunar exploration rover after hibernation at every lunar night. The test is designed to include a batch of Commercial lithium-ion cells from different manufacturers, with different nameplate capacities and different States of Charge. The cell behaviour during the test is monitored in-situ using cell terminal voltage measurements. To comprehend the effect of exposure to extreme low temperatures some complementary tests like visual examination, dimensional measurements, Residual Gas Analysis to detect any leakage, electrical tests to appraise electrical performance and 3 dimensional x-ray computed tomography analysis to view cell internal features are carried out at ambient conditions on cells both prior-to and after soaking at low temperatures. Results indicate successful survivability of tested cells after extreme thermal soak without any significant physical or internal damage or electrical performance degradation. Variation in cell terminal voltage with temperature is a reversible change attributed to the reversible phenomenon of freezing of cell electrolyte which furthermore is confirmed through ex-situ measurement of freezing point of electrolyte extracted from tested cells.
The conclusions drawn from the study are listed below,
- All the selected COTS 18650 Li-ion cells under the tested circumstances are capable of surviving extreme low temperature soak as harsh as −160°C for 336h or 14 days.
- All the tested cells do not show any degradation in electrical performance due to low temperature soak.
- The exposure to low temperatures under test conditions does not cause any physical damages, swelling, electrolyte leak or internal damage to electrode jelly-roll.
- The cells irrespective of initial State of Charge survive low temperature exposure
www.hindustantimes.com
