He looked at the arc between the Earth and Mars, and the words "Hohmann Transfer" and "26 months" marked on the arc.
There are several points on that arc, which are the Orbital Refueling nodes and transfer windows just marked by Elon Musk.
But his eyes stopped at the middle section of the arc - nothing was marked there, but that line represented the most vulnerable part of the entire Mars plan.
"Elon, how do you plan to solve the communication between Mars and the Earth?"
Elon Musk was picking up the water bottle from the table and paused for a beat.
He put down the water bottle, turned around and looked at the whiteboard, frowning slightly.
"Deep Space Network. NASA has three measurement and control stations in Goldstone, Madrid and Canberra. It is currently the only infrastructure that can support Mars communications.
But the bandwidth of the Deep Space Network is extremely limited - it takes several hours for the Mars detector to send back a high-resolution photo.
If there are one million people on Mars, communication through the deep space network is simply impossible. The bandwidth is not enough and the delay is too long."
"So in the Mars colonization plan, communication is an unsolved problem."
Zhao Chen moved his hand away from the arc and drew a new circle in the blank space of the whiteboard.
That circle is between the earth and Mars, located somewhere on the side of the earth.
Elon Musk looked at the circle he drew and said nothing.
"You mentioned Starlink's networking plan before. Forty-two thousand satellites, global broadband coverage.
If this plan is completed, the communication bandwidth between Mars and the earth will not need to rely on the deep space network.
Starlink's laser link can relay signals between planets.
The communication delay between the earth and Mars is only twenty minutes at most. If the orbital layout of Starlink matches the geometric relationship of the Mars transfer window--"
Elon Musk suddenly leaned forward.
His eyes changed--it was not the concentration in a technical discussion just now, but something rarer, something close to being ignited.
He walked to the whiteboard, took the red pen from Zhao Chen's hand, and drew a few points on the arc.
"I have discussed the idea you just mentioned internally, but no one has come in from your perspective.
The core of Starlink is not to provide broadband to the earth, but to provide communications to the entire solar system.
The direct communication between the earth and Mars is interfered by solar radiation, the signal is severely attenuated, and the bandwidth of the deep space network is extremely limited.
But if the satellites of Starlink form a laser relay network between the earth's orbit and the orbit of Mars - each satellite is a communication node -
The communication bandwidth between ground and fire can be improved by several orders of magnitude.
By that time, the base on Mars can communicate with any corner of the earth in real time.
It's not narrowband with a twenty-minute delay, it's broadband that's close to real-time."
He put down the pen and turned around to look at Zhao Chen.
"Zhao, you just connected the Starlink and Mars plans together.
I have never drawn pictures like this internally.
Starlink is the communication system, Starship is the transportation system, and Optimus is the labor system.
These three systems are indispensable under the framework of Mars colonization--
Starship sends people there, Optimus builds the infrastructure, and Starlink connects people to the earth.
You helped me fill in the last piece of this picture today at Boca Chica."
Zhao Chen returned to the table, picked up the already cool tea and took a sip.
"In the previously public description of your Starlink plan, you only mentioned global broadband coverage.
If the goal of relaying communications to Mars is written into the roadmap of Starlink, the magnitude of the entire plan will be completely different.
The networking of 42,000 satellites is not the end, but the starting point.
Earth orbit, Mars orbit, Lagrange point between earth and fire - satellite nodes can be arranged at each position.
Starlink transforms from communications network to solar system communications infrastructure."
Elon Musk stood in front of the whiteboard and was silent for several seconds.
He looked down at the points he had just drawn, then picked up the pen and wrote a line of words next to the arc - "Deep Space Laser Relay".
Then he turned around, faced Zhao Chen, and spoke in a very quiet tone that Zhao Chen rarely heard from him.
"Zhao, you have been at this base for less than three hours.
You just looked at the ring section of SN8 and the test video of the vacuum version of the Raptor.
Then you can tell me that Starlink is not just a communication network, it is the communication infrastructure of the solar system."
He put the red pen in the whiteboard slot, walked back to the folding table, and took another bottle of water from the refrigerator.
I unscrewed the cap but didn't drink. I just felt the condensed water droplets on the wall of the bottle with my palm.
"I have discussed this sentence internally countless times, but no one has ever connected it with the Mars plan in this way. You really surprised me."
"Mainly because the logic is there, but when most people look at Starlink, they only see broadband services in Earth orbit."
Zhao Chen put the tea cup on the table, stood up, walked to the whiteboard, and picked up the red pen from the whiteboard slot.
He added a few strokes next to the arc drawn by Elon Musk - a circle was drawn outside the Earth's orbit and marked "LEO Relay";
Mars draws a circle on the outside of the orbit, labeled "Mars Orbit";
A dotted line is drawn between the two circles, labeled "L4/L5 Relay".
Then an arrow was added at the end of the arc, pointing to the Mars surface.
"Starlink's current networking plan focuses on low-Earth orbit, with 42,000 satellites covering global broadband.
However, satellites in low-Earth orbit have a short lifespan and need to continue to repair the network. Moreover, when communicating directly with Mars from low-Earth orbit, the signal attenuation is too serious.
If you want to establish a stable communication link between Mars and the earth, satellite nodes need to be deployed in the relay orbit--
The Earth-Moon Lagrangian point, the Sun-Earth Lagrangian point, and even the Lagrangian point of the Mars orbit.
Each relay satellite is equipped with a laser communication terminal, forming a laser communication backbone network between planets.
Users on the earth access through low-Earth orbit Starlink, and the signal is uploaded to the relay node.
The laser link passing through the Lagrange point jumps to the Mars orbit, and then goes down to the terminal on the surface of Mars.
The latency of the entire link depends on the geometric distance between the planets, but the bandwidth and stability far exceed existing deep space networks."
Elon Musk put the water bottle on the table, took the red pen from Zhao Chen, and drew a question mark next to "L4/L5 Relay".
"How to solve the energy problem for relay satellites at Lagrange points?
At L4 or L5, the Solar Energy panel is further away from the sun, and the power generation efficiency will decrease.
Moreover, the alignment accuracy of laser communication terminals in deep space environments is extremely high, and satellites require high-power propulsion systems to maintain attitude and orbital position."
"Nuclear power source. Radioisotope thermoelectric generator, or small fission reactor.
SpaceX is already doing research on nuclear thermal propulsion, and the technical route for nuclear power is ready.
As for laser alignment accuracy - Starlink's existing laser link has verified high-precision alignment between satellites in low orbit.
The distance of the Lagrangian point is farther, but the angular velocity of the alignment is slower, which makes fast tracking easier than that of low-orbit satellites."
Zhao Chen Put the red pen back into the whiteboard slot, step back and look at the whole picture.
"Communication is only the first step. If the relay network is built, the base on Mars can communicate with any corner of the earth in real time.
Telemedicine, distance education, remote engineering support - all scenarios that require real-time interaction can be implemented on Mars.
By that time, engineers at the Mars base can directly connect via video with experts on Earth if they encounter technical problems.
Children on Mars can take online classes on Earth.
Mars colonization is no longer about 'throwing people over to fend for themselves', it is an outpost that maintains a real-time connection with the earth."
Elon Musk stared at the picture on the whiteboard that was repeatedly redacted by two people for several seconds.
Then he turned around and faced Zhao Chen, with something in his expression that Zhao Chen had never seen on his face before.
The sky outside has darkened, and the ceiling light in the factory illuminates the whiteboard slightly.
In the distance, an engineer began to clear away the tool table. The sound of the angle grinder stopped, leaving only the sound of low-frequency current coming from a corner.
Elon Musk sent them to the door of the factory. The headlights of the black Model X were on in the dusk.
He stood under the door frame, put his hands in his pockets, and watched Zhao Chen open the car door. Then he suddenly spoke.
"Zhao, if SN8 flies successfully, when you come to Boca Chica again, I will take you to the launch pad.
Stand next to SN8 and you will see how much higher that Stainless Steel Water Tower has become."
Zhao Chen looked back at him. "I will come."