What difficulties are there to overcome when going from “cold launch” at sea to “hot launch” at sea?

On the afternoon of December 9, in the Yellow Sea, the Jielong-3 solid-fuel carrier rocket ignited and took off from the launch ship in a hot launch at sea, and then sent 14 satellites into the predetermined orbit. The rocket's first flight mission was a complete success. In this mission, China's rocket achieved a leap from cold launch at sea to hot launch at sea.

The moment of the Jielong-3 rocket launch

Let’s first talk about what cold launch and hot launch are.

A cold launch means that the rocket is first ejected from the launch tube and then ignites and takes off in mid-air. The high-temperature tail flame of the rocket will not burn the launch platform. This is the launch method used by the Long March 11 carrier rocket. A hot launch means that the rocket ignites and takes off directly from the launch platform without the ejection process. This is the launch method used by the vast majority of my country's rockets.

So why try cold launch and hot launch at sea? In fact, this is related to the advantages of launching at sea.

First, the sea launch platform can be deployed flexibly and can be launched in the sea near the equator, making the most of the speed of the earth's rotation to send the rocket into orbit. This can increase the payload of the launch vehicle and save the fuel of the launch vehicle.

Second, sea launches have the advantage of a wide range of launch targets, and rocket debris can splash down on the sea surface, avoiding densely populated areas such as cities, and the landing area is safe. If the launch is from a traditional land launch site, then the impact of the debris splashing down on the densely populated areas around the launch site must be considered.

It seems that hot launch at sea is simpler than cold launch at sea because it has one less catapult step.

Direct ignition of the rocket will produce a strong reaction force, and the high-temperature tail flame of the rocket will also test the bearing capacity of the launch ship and launch equipment.

So, how to solve these problems? Ouyang Song, deputy chief designer of the ground launch support system of the Jielong-3 rocket, explained this.

"Offshore hot launch technology is the inheritance and development of offshore cold launch technology," said Ouyang Song.

When watching the video of the first flight mission of the Jielong-3 rocket, careful viewers may find that before the rocket took off, it was wrapped in a rectangular "cage", which is the guide frame.

The sea is windy and the waves are high. Without external support, it is difficult for the rocket to stand steadily on the launch ship. Therefore, during cold launch, the launch tube supports the stability of the rocket; during hot launch, the rocket relies on the guide frame. The guide frame can "hold" the rocket and prevent it from becoming unstable and overturning due to sea conditions.

As we mentioned earlier, when a rocket is hot-launched at sea, it will ignite and take off directly from the launch ship, which will test the launch ship's ability to withstand high temperatures. Ouyang Song introduced that in response to this problem, the developers added a 15-meter-long and 10-meter-wide launch support platform at the tail of the launch ship. With the help of this platform, the rocket tail flame will be directed from top to bottom to the horizontal sides, greatly reducing the impact of the rocket tail flame on the launch ship and launch equipment.

Not only that, the developers also added a second layer of insurance for the launch equipment - for the core components, they took the approach of adding a protective layer to protect them; and added protective steel plates in areas that are subject to high heat flux density.

"Our goal is to ensure that after the rocket is launched, the main structure of the equipment is not affected and that it can perform the mission again after simple maintenance," said Ouyang Song.

Since there are so many challenges to overcome in offshore thermal launch, why should we try it?

Ouyang Song said that although hot launch at sea is difficult, it is more economical than cold launch at sea. "For example, the cost of the launch tube is higher than that of the guide frame, and cold launch at sea requires more disposable consumables than hot launch at sea."

In Ouyang Song's view, what is more important is that hot launch at sea absorbs the advantages of cold launch at sea and eliminates its disadvantages, thus maximizing its value.

With the success of the hot launch of the Jielong-3 rocket at sea, we may see more types of rockets attempt hot launch at sea in the future.