At this moment, Xu Ruoxi, Dang Zhongcheng and the others all looked at Li Chen in bewilderment.

They heard Li Chen talking to himself.

Everyone has a puzzled look on their faces.

At the same time, I was a little nervous.

Only at this moment, the army of zombies outside is still attacking.

Constantly attack the fourth layer of defense barriers.

If you don't stop them, let them break through this fourth barrier.

Then they will directly break into the underground command center.

The underground command center is equivalent to the brain part of the star shelter.

If it is attacked here, the consequences will be disastrous.

Hearing the words of his subordinates at this time, Li Chen also came back to his senses.

Looking up at the crowd, he himself was slightly puzzled.

But immediately Li Chen thought of something.

It seems that only he can see the illusory selection interface in front of him.

Including Dang Zhongcheng and Xu Ruoxi, they couldn't see it.

This may be Noah's self-protection function.

After all, not everyone has Li Chen's authority.

If he wanted to operate the entire star refuge, of course Li Chen had to come in person.

"nothing."

"Wait for me a moment, I'm discussing something with Noah."

Li Chen nodded, and then communicated with Noah in his mind.

"Noah, think of a way to explain it to everyone."

"I'm afraid they won't be able to accept such a sudden upgrade of the star shelter."

"It's too magical for them after all."

Li Chen ordered.

[Host please rest assured, just leave this matter to me to explain. 】

[Please make your upgrade choice as soon as possible, the fourth barrier of protection can only persist for another 9 minutes at most. 】

After Noah reminded, he began to broadcast through the internal broadcast of the star shelter.

Start to explain to all the residents and fighters.

Li Chen didn't listen carefully to how it was explained.

At this moment, all attention is placed on the selection interface in front of him.

"Because resources are limited, each design approach addresses different trade-offs."

In the selection interface in front of you, there are a total of about twenty upgrade options.

And he quickly figured out the difference between these design drawings.

"For example, the first design drawing focuses on protecting the command center of the star shelter."

"So on the preview picture, you can clearly see that the command center of the star shelter has been fully reinforced after the upgrade."

"The location and functional attributes of each floor remain the same, but the bottom few layers of shelters, all the protective barriers have been reinforced, from the original 1.5 meters thick mixed heavy metal barriers, increased to 4.5 meters."

"The defense has been strengthened by about three times."

Li Chen thought quickly, and then set his sights on the second upgrade preview.

This upgrade preview focuses on strengthening the weapon production base, military training base, scientific research area, and the area where the core processor is located.

At the same time, take into account the strengthening of the underground command center.

But the same, because the energy and resources consumed by the overall upgrade are limited.

Therefore, the reinforcement of the above key areas is an average reinforcement.

The thickness of the protective barriers in each area has increased from the original 1.5 meters to about 3.0 meters.

As for the thickness of other regional protective barriers, it remains unchanged.

Li Chen is not particularly satisfied with these trade-off designs.

He tossed and turned, and finally his eyes fell on the seventh design drawing.

"This one looks pretty good."

This is a design drawing that fully considers the star shelter.

No area was abandoned, and no area was focused on strengthening.

It evenly distributes all upgrade resources to the entire star shelter.

Not only are newer composite heavy metal materials with higher defense strength used.

At the same time, the thickness of the composite heavy metal materials has also increased from 1.5 meters to 2.5 meters.

Another piece of good news is that after the upgrade of the star shelter.

All protective doors, as well as the internal single-layer protective barriers.

All crafted from a unique composite supermetal.

The defense will be much stronger than the original ordinary composite heavy metal.

"That's it!"

Li Chen looked at the time.

It's just such a short time for me to make a choice.

Another three minutes passed.

The zombies that broke in from the ground outside are still attacking.

The fourth layer of protective barriers is already crumbling.

Only six minutes at most.

[The host confirms the choice of design blueprint 7, and upgrade your star shelter according to this choice? 】

[Once the upgrade operation is selected, it cannot be changed. It is estimated that the entire upgrade process will take about 30 seconds! 】

Noah's reminder sounded in his mind.

Li Chen thought for a while and nodded immediately.

"No problem! Let's upgrade according to the style of this design drawing!"

He rubbed his hands together.

After the star shelter is upgraded, other strengthening operations can be performed on it.

And just now Noah made it clear.

This strengthening operation can be DIY by yourself.

The degree of freedom is very high.

Li Chen was very curious about how to strengthen it.

At the same time, he also remembered that there was an unused super gift bag in his system backpack.

[Choose success! The energy crystal cores required to upgrade the star shelters have been automatically deducted for you! 】

【Host please wait...】

Noah started the countdown.

At the same time, Li Chen and others immediately felt that changes visible to the naked eye began to appear in the entire star refuge.

"This is…"

"Has the upgrade started yet?"

"It's about to start! The road to upgrade and strengthen the star shelter!"

"The protection level will be stronger than before! Those **** zombies outside, it's time for us to fight back!"

Just now, Noah has explained everything to all members.

Although Li Chen didn't know how it was explained to everyone.

But at the moment, it looks like everyone has fully accepted it.

Did not show any surprise or anxiety and doubt.

Seeing this scene, Li Chen didn't speak.

He carefully observed the changes in the entire star refuge.

At this time, they were in the original underground command center of the Star Refuge.

As Noah upgraded the star shelter.

The original silver-gray and dark refuge background was quickly replaced by a matte silver.

And those protective barriers, just from the surface, are by no means inferior.

All are made of composite supermetal materials that people have never seen before.

What shocked everyone even more.

In addition to the improvement of the overall protection level of the star shelter.

At this moment, its size is also rapidly increasing!

a moment later...

[The star shelter has been successfully upgraded! 】

[The level of the current star shelter has been upgraded to 1 star, and the capacity of the shelter has been expanded from 200,000 people to 500,000 people! 】